This is my Deploy-log after enabling Gatsby incremental builds. Why is it so slow?

Netlify +Gatsby incremental build ultra slow

9:36:08 AM: Build ready to start
9:36:10 AM: build-image version: 2dbd444fcdce00cf06325060a8238d5ae3e86774
9:36:10 AM: build-image tag: v3.3.7
9:36:10 AM: buildbot version: d305548225ac57bb00eb5a596b0b8674e76a4681
9:36:11 AM: Fetching cached dependencies
9:36:11 AM: Starting to download cache of 539.6MB
9:36:15 AM: Finished downloading cache in 3.835745556s
9:36:15 AM: Starting to extract cache
9:36:38 AM: Finished extracting cache in 23.20002401s
9:36:38 AM: Finished fetching cache in 27.178025455s
9:36:38 AM: Starting to prepare the repo for build
9:36:38 AM: Preparing Git Reference refs/heads/master
9:36:41 AM: Different functions path detected, going to use the one specified in the Netlify configuration file: 'lambda' versus '' in the Netlify UI
9:36:41 AM: Creating functions prep folder
9:36:41 AM: Starting build script
9:36:41 AM: Installing dependencies
9:36:41 AM: Started restoring cached node version
9:36:48 AM: Finished restoring cached node version
9:36:49 AM: v10.20.1 is already installed.
9:36:52 AM: Now using node v10.20.1 (npm v6.14.4)
9:36:52 AM: Attempting ruby version 2.6.2, read from environment
9:36:53 AM: Using ruby version 2.6.2
9:36:54 AM: Using PHP version 5.6
9:36:54 AM: Started restoring cached node modules
9:36:54 AM: Finished restoring cached node modules
9:36:54 AM: Started restoring cached yarn cache
9:36:54 AM: Finished restoring cached yarn cache
9:36:55 AM: Installing NPM modules using Yarn version 1.9.4
9:36:55 AM: yarn install v1.9.4
9:36:56 AM: [1/4] Resolving packages...
9:36:57 AM: [2/4] Fetching packages...
9:36:57 AM: (node:1211) [DEP0005] DeprecationWarning: Buffer() is deprecated due to security and usability issues. Please use the Buffer.alloc(), Buffer.allocUnsafe(), or Buffer.from() methods instead.
9:37:26 AM: info fsevents@2.1.3: The platform "linux" is incompatible with this module.
9:37:26 AM: info "fsevents@2.1.3" is an optional dependency and failed compatibility check. Excluding it from installation.
9:37:26 AM: info fsevents@1.2.13: The platform "linux" is incompatible with this module.
9:37:26 AM: info "fsevents@1.2.13" is an optional dependency and failed compatibility check. Excluding it from installation.
9:37:26 AM: [3/4] Linking dependencies...
9:37:26 AM: warning "gatsby > @pmmmwh/react-refresh-webpack-plugin@0.2.0" has unmet peer dependency "sockjs-client@^1.4.0".
9:37:26 AM: warning "gatsby > react-hot-loader@4.12.21" has unmet peer dependency "@types/react@^15.0.0 || ^16.0.0".
9:37:26 AM: warning "gatsby > @typescript-eslint/eslint-plugin > tsutils@3.17.1" has unmet peer dependency "typescript@>=2.8.0 || >= 3.2.0-dev || >= 3.3.0-dev || >= 3.4.0-dev || >= 3.5.0-dev || >= 3.6.0-dev || >= 3.6.0-beta || >= 3.7.0-dev || >= 3.7.0-beta".
9:37:26 AM: warning "gatsby > gatsby-cli > ink@2.7.1" has unmet peer dependency "@types/react@>=16.8.0".
9:37:26 AM: warning "gatsby > gatsby-cli > gatsby-recipes > ws@7.2.5" has unmet peer dependency "bufferutil@^4.0.1".
9:37:26 AM: warning "gatsby > gatsby-cli > gatsby-recipes > ws@7.2.5" has unmet peer dependency "utf-8-validate@^5.0.2".
9:37:26 AM: warning "gatsby-plugin-netlify > webpack-assets-manifest@3.1.1" has unmet peer dependency "webpack@>=4.4.0".
9:37:26 AM: warning "gatsby-plugin-sass > sass-loader@7.3.1" has unmet peer dependency "webpack@^3.0.0 || ^4.0.0".
9:37:27 AM: warning " > lodash-webpack-plugin@0.11.5" has unmet peer dependency "webpack@^2.0.0 || ^3.0.0 || ^4.0.0".
9:37:27 AM: warning "netlify-cms-app > netlify-cms-widget-code@1.1.4" has unmet peer dependency "codemirror@^5.46.0".
9:37:27 AM: warning "netlify-cms-app > netlify-cms-widget-relation@2.6.0" has unmet peer dependency "netlify-cms-lib-widgets@^1.0.0".
9:37:27 AM: warning "netlify-cms-app > netlify-cms-widget-code > react-codemirror2@6.0.1" has unmet peer dependency "codemirror@5.x".
9:37:27 AM: warning "netlify-cms-app > netlify-cms-core > redux-notifications > react-redux@4.4.10" has incorrect peer dependency "redux@^2.0.0 || ^3.0.0".
9:37:27 AM: warning " > netlify-cms-media-library-cloudinary@1.3.4" has unmet peer dependency "netlify-cms-lib-util@^2.1.3-beta.0".
9:37:47 AM: [4/4] Building fresh packages...
9:37:55 AM: Done in 60.06s.
9:37:56 AM: NPM modules installed using Yarn
9:37:56 AM: Started restoring cached go cache
9:37:56 AM: Finished restoring cached go cache
9:37:56 AM: unset GOOS;
9:37:56 AM: unset GOARCH;
9:37:56 AM: export GOROOT='/opt/buildhome/.gimme/versions/go1.12.linux.amd64';
9:37:56 AM: export PATH="/opt/buildhome/.gimme/versions/go1.12.linux.amd64/bin:${PATH}";
9:37:56 AM: go version >&2;
9:37:56 AM: export GIMME_ENV='/opt/buildhome/.gimme/env/go1.12.linux.amd64.env';
9:37:56 AM: go version go1.12 linux/amd64
9:37:56 AM: Installing missing commands
9:37:56 AM: Verify run directory
9:37:58 AM: ​
9:37:58 AM: ┌─────────────────────────────┐
9:37:58 AM: │        Netlify Build        │
9:37:58 AM: └─────────────────────────────┘
9:37:58 AM: ​
9:37:58 AM: ❯ Version
9:37:58 AM:   @netlify/build 0.4.11
9:37:58 AM: ​
9:37:58 AM: ❯ Flags
9:37:58 AM:   mode: buildbot
9:37:58 AM: ​
9:37:58 AM: ❯ Current directory
9:37:58 AM:   /opt/build/repo
9:37:58 AM: ​
9:37:58 AM: ❯ Config file
9:37:58 AM:   /opt/build/repo/netlify.toml
9:37:58 AM: ​
9:37:58 AM: ❯ Context
9:37:58 AM:   production
9:37:58 AM: ​
9:37:58 AM: ❯ Installing plugins
9:37:58 AM:    - netlify-plugin-gatsby-cache
9:39:03 AM: ​
9:39:03 AM: ❯ Loading plugins
9:39:03 AM:    - netlify-plugin-gatsby-cache@0.2.1
9:39:03 AM: ​
9:39:03 AM: ┌───────────────────────────────────────────────────────────┐
9:39:03 AM: │ 1. onPreBuild command from @netlify/plugin-functions-core │
9:39:03 AM: └───────────────────────────────────────────────────────────┘
9:39:03 AM: ​
9:39:03 AM: ​
9:39:03 AM: (@netlify/plugin-functions-core onPreBuild completed in 11ms)
9:39:03 AM: ​
9:39:03 AM: ┌────────────────────────────────────────────────────────┐
9:39:03 AM: │ 2. onPreBuild command from netlify-plugin-gatsby-cache │
9:39:03 AM: └────────────────────────────────────────────────────────┘
9:39:03 AM: ​
9:39:04 AM: Found a Gatsby cache. We’re about to go FAST. ⚡️
9:39:04 AM: ​
9:39:04 AM: (netlify-plugin-gatsby-cache onPreBuild completed in 447ms)
9:39:04 AM: ​
9:39:04 AM: ┌────────────────────────────────────┐
9:39:04 AM: │ 3. build.command from netlify.toml │
9:39:04 AM: └────────────────────────────────────┘
9:39:04 AM: ​
9:39:04 AM: $ npm run build
9:39:04 AM: > gatsby-starter-netlify-cms@1.1.3 build /opt/build/repo
9:39:04 AM: > run-p build:**
9:39:04 AM: > gatsby-starter-netlify-cms@1.1.3 build:app /opt/build/repo
9:39:04 AM: > GATSBY_EXPERIMENTAL_PAGE_BUILD_ON_DATA_CHANGES=true npm run clean && gatsby build
9:39:04 AM: > gatsby-starter-netlify-cms@1.1.3 build:lambda /opt/build/repo
9:39:04 AM: > netlify-lambda build src/lambda
9:39:05 AM: > gatsby-starter-netlify-cms@1.1.3 clean /opt/build/repo
9:39:05 AM: > gatsby clean
9:39:05 AM: netlify-lambda: Building functions
9:39:06 AM: 
9:39:06 AM: info Deleting .cache, public
9:39:06 AM: info Successfully deleted directories
9:39:07 AM: Hash: 642381b00c541cec97dd
9:39:07 AM: Version: webpack 4.43.0
9:39:07 AM: Time: 1200ms
9:39:07 AM: Built at: 05/08/2020 7:39:07 AM
9:39:07 AM:    Asset     Size  Chunks             Chunk Names
9:39:07 AM: hello.js  1.2 KiB       0  [emitted]  hello
9:39:07 AM: Entrypoint hello = hello.js
9:39:07 AM: [0] ./hello.js 777 bytes {0} [built]
9:39:08 AM: 
9:39:08 AM: success open and validate gatsby-configs - 0.072s
9:39:10 AM: success load plugins - 1.442s
9:39:10 AM: success onPreInit - 0.013s
9:39:10 AM: success delete html and css files from previous builds - 0.015s
9:39:10 AM: success initialize cache - 0.011s
9:39:10 AM: success copy gatsby files - 0.044s
9:39:10 AM: success onPreBootstrap - 0.009s
9:39:10 AM: success createSchemaCustomization - 0.019s
9:39:10 AM: success source and transform nodes - 0.271s
9:39:11 AM: 
9:39:11 AM: success building schema - 0.405s
9:39:11 AM: 
9:39:11 AM: success createPages - 0.093s
9:39:11 AM: success createPagesStatefully - 0.096s
9:39:11 AM: success onPreExtractQueries - 0.001s
9:39:11 AM: 
9:39:11 AM: success update schema - 0.042s
9:39:11 AM: success extract queries from components - 0.467s
9:39:11 AM: 
9:39:11 AM: success write out requires - 0.005s
9:39:11 AM: success write out redirect data - 0.086s
9:39:11 AM: 
9:39:11 AM: success onPostBootstrap - 0.001s
9:39:11 AM: 
9:39:11 AM: ⠀
9:39:11 AM: info bootstrap finished - 5.675 s
9:39:11 AM: ⠀
9:39:59 AM: 
9:39:59 AM: gatsby-plugin-purgecss: Only processing  /opt/build/repo/src/components/all.sass
9:40:14 AM: 
9:40:14 AM: success Building production JavaScript and CSS bundles - 61.219s
9:40:15 AM: 
9:40:15 AM: success Rewriting compilation hashes - 0.001s
9:40:16 AM: success run queries - 64.184s - 30/30 0.47/s
9:40:23 AM: 
9:40:23 AM: 
9:40:23 AM: 
9:40:23 AM: gatsby-plugin-purgecss:
9:40:23 AM: 
9:40:23 AM: 
9:40:23 AM:  Previous CSS Size: 156.93 KB
9:40:23 AM: 
9:40:23 AM: 
9:40:23 AM:  New CSS Size: 9.15 KB (-94.17%)
9:40:23 AM: 
9:40:23 AM: 
9:40:23 AM:  Removed ~147.78 KB of CSS
9:40:23 AM: 
9:40:23 AM: 
9:40:25 AM: success Building static HTML for pages - 2.055s - 27/27 13.14/s
9:40:25 AM: success Generating image thumbnails - 73.663s - 85/85 1.15/s
9:40:25 AM: success onPostBuild - 0.043s
9:40:25 AM: info Done building in 79.47 sec
9:40:25 AM: ​
9:40:25 AM: (build.command completed in 1m 22s)
9:40:25 AM: ​
9:40:25 AM: ┌────────────────────────────────────────────────────────────┐
9:40:25 AM: │ 4. onPostBuild command from @netlify/plugin-functions-core │
9:40:25 AM: └────────────────────────────────────────────────────────────┘
9:40:25 AM: ​
9:40:25 AM: Packaging functions from lambda
9:40:26 AM: Functions packaged in /tmp/zisi-5eb50be828a0620007985e6e
9:40:26 AM:  - hello.zip
9:40:26 AM: ​
9:40:26 AM: (@netlify/plugin-functions-core onPostBuild completed in 98ms)
9:40:26 AM: ​
9:40:26 AM: ┌─────────────────────────────────────────────────────────┐
9:40:26 AM: │ 5. onPostBuild command from netlify-plugin-gatsby-cache │
9:40:26 AM: └─────────────────────────────────────────────────────────┘
9:40:26 AM: ​
9:40:26 AM: Stored the Gatsby cache to speed up future builds.
9:40:26 AM: ​
9:40:26 AM: (netlify-plugin-gatsby-cache onPostBuild completed in 523ms)
9:40:26 AM: ​
9:40:26 AM: ┌─────────────────────────────┐
9:40:26 AM: │   Netlify Build Complete    │
9:40:26 AM: └─────────────────────────────┘
9:40:26 AM: ​
9:40:26 AM: (Netlify Build completed in 2m 28.4s)
9:40:26 AM: Caching artifacts
9:40:26 AM: Started saving node modules
9:40:26 AM: Finished saving node modules
9:40:26 AM: Started saving yarn cache
9:40:26 AM: Finished saving yarn cache
9:40:26 AM: Started saving pip cache
9:40:39 AM: Finished saving pip cache
9:40:39 AM: Started saving emacs cask dependencies
9:40:39 AM: Finished saving emacs cask dependencies
9:40:39 AM: Started saving maven dependencies
9:40:39 AM: Finished saving maven dependencies
9:40:39 AM: Started saving boot dependencies
9:40:39 AM: Finished saving boot dependencies
9:40:39 AM: Started saving go dependencies
9:40:39 AM: Finished saving go dependencies
9:40:39 AM: Build script success
9:40:39 AM: Starting to deploy site from 'public'
9:40:39 AM: Creating deploy tree 
9:40:39 AM: Creating deploy upload records
9:40:40 AM: 41 new files to upload
9:40:40 AM: 0 new functions to upload
9:40:42 AM: Starting post processing
9:40:46 AM: Post processing done
9:40:46 AM: Site is live
9:42:16 AM: Finished processing build request in 6m5.517168316s