@pluffmud Apologies, I misread that it was connected to port 3 on your router (which does not matter, BTW).
You might want to try this script, that should get you going to enable VLANs at least and keep your network functional. You can then split off ports to your liking.
The failsafe feature in the web UI might be triggering prematurely but I can't tell, I seldom use it and certainly not for low-level configuration.