I have this same issue starting yesterday.
The GUI became inaccessible as soon as I started the array after a reboot. All my dockers started up and were accessible, SSH and MC were usable.
I have connected with Unraid Connect, and get "request to http://127.0.0.1/graphql failed, reason: connect ECONNREFUSED 127.0.0.1:80" under Storage, Docker Apps, and Vitual Machines.
I haven't tried safe mode yet.
I will post diagnostics later if I can.
Any other help or suggestions would be appreciated.