Sometimes, after update OS, this setting is reset, so you have to modify it again.
Copy from this thread on AskUbuntu
Check your WiFi MTU, using
ip link
also notice your WiFi interface's name.
The MTU (Maximum Transmission Unit) is the size of the largest packet that can be sent in a single network transmission. If a packet exceeds the MTU of a link, the data must be split into multiple packets (fragmented). These multiple packets must be sent over the link, received, acknowledged, and reassembled at the far end. If your link is misconfigured, and you have to fragment every packet you send, your actual data transfer rate drops.
Ethernet (wired) networks use an MTU of 1500 bytes.
Due to additional per packet overhead for WiFi (8 bytes PPPoE header), WiFi uses an MTU of 1492.
Your MTU should be set by your DHCP server, check your router's config.
You can set your own MTU (setting does not persist over restarts) with
sudo ip link set dev name mtu 1492
where "name" is the interface name from above.
Here's an example:
walt@squid:~(0)$ ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp63s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN mode DEFAULT group default qlen 1000
link/ether 00:24:21:7f:e5:1c brd ff:ff:ff:ff:ff:ff
3: wlxf46d04b1790f: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN mode DORMANT group default qlen 1000
link/ether f4:6d:04:b1:79:0f brd ff:ff:ff:ff:ff:ff
walt@squid:~(0)$ sudo ip link set dev wlxf46d04b1790f mtu 1492
[sudo] password for walt:
walt@squid:~(0)$ ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp63s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN mode DEFAULT group default qlen 1000
link/ether 00:24:21:7f:e5:1c brd ff:ff:ff:ff:ff:ff
3: wlxf46d04b1790f: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1492 qdisc mq state UP mode DORMANT group default qlen 1000
link/ether f4:6d:04:b1:79:0f brd ff:ff:ff:ff:ff:ff
My WiFi "interface name" is "wlxf46d04b1790f".
NOTE: packet fragmentation is not logged, as it's a "feature" of the Data Link layer (layer 2 in the OSI model).