Story:
Decided to futz with my unRaid hardware for the first time in probably 3yrs. Something gets caught, USB gets bent, drive no longer recognized. I have no idea where I saved my most recent USB backup, but it wouldn't be up-to-date anyway. However I do find one of my first backups in Google Drive. I haven't changed hardware since the original build, so I decided to give it a shot. Burn it to a USB with the unRaid Tool [which is AMAZINGLY simple, shout out to the devs], and boot. Go to register the new key but it won't take. OS too old was my thought, better upgrade. Couldn't access the upgrade server, which is when I started to worry.
Problem:
Exact some symptoms as you. Network failure errors. I realized it wasn't AWS issue after clicking the Apps tab and getting some error about not being connected to the internet. Which was odd because I was connecting to unRaid via a browser.
Solution:
Turn off manual IPv4 address assignment. An earlier Si1 video, which I follow to the letter, changed address management from automatic to manual. Even though I rebooted my router, I thought there might be an unresolved address conflict in the router DHCP table.
Setttings Tab ⇨ IPv4 address assignment ⇨ Automatic
Didn't even have to reboot. Everything came back to life, even though my router didn't assign unRaid a new IP. Why it worked I may never know, but I hope your solution is just as simple.