Intermittent issues suck so much! They're hard to diagnose and often even harder to fix...

To be honest, I have no idea why that would be occurring and it's certainly not something that anybody has reported previously. Networking not working at all is something that can happen if you install to hardware and the hardware is particularly new and/or requires non-free drivers, but I've not come across intermittent issues.

Having said that, I have heard of similar issues on Linux if the system has a hard time working out which driver should be used and sometimes loads the wrong one. Apparently the way to work around that is to blacklist the driver that doesn't work.

If I'm on the right track (which I may or may not be) then checking the driver loaded (both when working and when not) then hopefully that may give some insight?

You should be able to get info about networking hardware using the 'lshw' command. First install like this (you'll need networking to be working):

apt update && apt install -y lshw

Then get network hardware info like this:

lshw -C network

You'll find the driver info to the right of the "configuration:" section. Please feel free to post output if you want a hand interpreting it.

Another way to get some more info about your hardware is using the 'lspci' tool. Again you'll also need to install the relevant package:

apt update && apt install -y pciutils

Then get the info like this:

lspci -nnk | grep -iA2 net

This second approach will note the driver in use too, but will also give a vendor/product code (e.g. my laptop wifi adaptor is '[8086:0085]'). You can use that to search the internet for people expericing ismilar issues which might give some insight? Again, feel free to share if you want furher input from me.