I'm not sure what I'm doing wrong with FlatBuffers... (note, directories in filenames are noted by dashes since GH doesn't allow slashes, so myGame-replay.go should be at myGame/replay.go)

main.go

package main

import (
	"io/ioutil"
	"log"

  "myGame/replay"
)

func main() {
	// Create a replay
	replayName := "MyAmazingReplay"

	rep := replay.Replay{
		Name: replayName,
		Events: []replay.Event{
			replay.Event{
				replay.Frame{
					Number: 0,
					Dt:     0.011112,
				},
			},
			replay.Event{
				replay.Frame{
					Number: 1,
					Dt:     0.008151,
				},
			},
		},
	}

	// Save it to disk
	if !rep.SaveToDisk() {
		panic("Save failed!")
	}

	// Read it back
	bytes, err := ioutil.ReadFile(replayName + "." + replay.ReplaySuffix)
	if err != nil {
		panic(err)
	}
	reloadedReplay, err := replay.NewReplay(bytes, replayName)
	if err != nil {
		panic(err)
	}

	// Print the contents
	log.Printf("%#v", reloadedReplay)
}

myGame-replay.fbs

namespace flatbuffers;

table Replay {
    events:[Event];
}

table Event {
    frame:Frame;
}

table Frame {
    number:int;
    dt:float64;
}

root_type Replay;

myGame-replay.go

// Package replay is concerned with the abilities for reading and writing replays.
package replay

import (
	"fmt"
	"io/ioutil"
	"log"
	"time"

	fb "myGame/replay/flatbuffers"

	flatbuffers "github.com/google/flatbuffers/go"
)

const ReplaySuffix = "replay"

type Replay struct {
	Name   string
	Events []Event
}

type Event struct {
	Frame Frame
}

type Frame struct {
	Number int32
	Dt     float64
}

func (r Replay) SaveToDisk() bool {
	builder := flatbuffers.NewBuilder(1024)

	eventOffsets := make([]flatbuffers.UOffsetT, 0, len(r.Events))
	for _, event := range r.Events {
		fb.FrameStart(builder)

		fb.FrameAddNumber(builder, event.Frame.Number)
		fb.FrameAddDt(builder, event.Frame.Dt)

		frameOffset := fb.FrameEnd(builder)

		fb.EventStart(builder)

		fb.EventAddFrame(builder, frameOffset)

		eventOffset := fb.EventEnd(builder)
		eventOffsets = append(eventOffsets, eventOffset)
	}

	fb.ReplayStartEventsVector(builder, len(r.Events))
	log.Println("len(r.Events)", len(r.Events))
	log.Println("len(eventOffsets)", len(eventOffsets))
	for i := len(eventOffsets) - 1; i >= 0; i-- {
		log.Println("i", i)
		builder.PrependUOffsetT(eventOffsets[i])
	}
	builder.EndVector(len(eventOffsets))
	fb.ReplayStart(builder)
	replayOffset := fb.ReplayEnd(builder)

	// Write to file.
	builder.Finish(replayOffset)
	buffer2 := builder.FinishedBytes()
	buffer := builder.Bytes[builder.Head():]
	log.Println("buffer2:   %#v", buffer2)

	if r.Name == "" {
		now := time.Now()
		r.Name = fmt.Sprintf("%04d-%02d-%02d--%02d-%02d-%02d", now.Year(), now.Month(), now.Day(), now.Hour(), now.Minute(), now.Second())
	}
	err := ioutil.WriteFile(r.Name+"."+ReplaySuffix, buffer, 0644)
	if err != nil {
		log.Printf("Error writing replay: %s", err)
	}

	log.Println("Writing len(buffer)", len(buffer))
	log.Println("Writing buffer", buffer)

	// Huge success.
	return true
}

func NewReplay(buf []byte, name string) (*Replay, error) {
	log.Println("Reading len(buf)", len(buf))
	log.Println("Reading buffer", buf)
	replayBuffer := fb.GetRootAsReplay(buf, 0)
	var replay Replay
	replay.Name = name

	eventLength := replayBuffer.EventsLength()
	replay.Events = make([]Event, eventLength)
	log.Printf("Number of events: %d", eventLength)
	for i := 1; i < eventLength; i++ {
		var event Event
		var eventBuffer fb.Event
		if !replayBuffer.Events(&eventBuffer, i) {
			return nil, fmt.Errorf("Failed to load event index %d", i)
		}

		// Handle Event
		var frameBuffer fb.Frame
		eventBuffer.Frame(&frameBuffer)

		// Handle Frame
		event.Frame.Number = frameBuffer.Number()
		event.Frame.Dt = frameBuffer.Dt()

		replay.Events[i] = event
	}

	return &replay, nil
}

output.txt

2018/11/23 08:36:13 len(r.Events) 2
2018/11/23 08:36:13 len(eventOffsets) 2
2018/11/23 08:36:13 i 1
2018/11/23 08:36:13 i 0
2018/11/23 08:36:13 buffer2:   %#v [12 0 0 0 0 0 0 0 4 0 4 0 4 0 0 0 2 0 0 0 48 0 0 0 4 0 0 0 222 255 255 255 12 0 0 0 8 0 18 0 12 0 40 8 0 0 0 117 4 112 179 120 177 128 63 1 0 0 0 0 0 6 0 8 0 4 0 6 0 0 0 12 0 0 0 8 0 12 0 0 0 4 0 8 0 0 0 122 198 190 100 227 193 134 63]
2018/11/23 08:36:13 Writing len(buffer) 96
2018/11/23 08:36:13 Writing buffer [12 0 0 0 0 0 0 0 4 0 4 0 4 0 0 0 2 0 0 0 48 0 0 0 4 0 0 0 222 255 255 255 12 0 0 0 8 0 18 0 12 0 40 8 0 0 0 117 4 112 179 120 177 128 63 1 0 0 0 0 0 6 0 8 0 4 0 6 0 0 0 12 0 0 0 8 0 12 0 0 0 4 0 8 0 0 0 122 198 190 100 227 193 134 63]
2018/11/23 08:36:13 Reading len(buf) 96
2018/11/23 08:36:13 Reading buffer [12 0 0 0 0 0 0 0 4 0 4 0 4 0 0 0 2 0 0 0 48 0 0 0 4 0 0 0 222 255 255 255 12 0 0 0 8 0 18 0 12 0 40 8 0 0 0 117 4 112 179 120 177 128 63 1 0 0 0 0 0 6 0 8 0 4 0 6 0 0 0 12 0 0 0 8 0 12 0 0 0 4 0 8 0 0 0 122 198 190 100 227 193 134 63]
2018/11/23 08:36:13 replay.Name: MyAmazingReplay
2018/11/23 08:36:13 Number of events: 0
2018/11/23 08:36:13 &replay.Replay{Name:"MyAmazingReplay", Events:[]replay.Event{}}

I needed to save the offset from L58 (the return value I wasn't getting) and add it to the main object between L59 and L60