Currently running 7.3.0-rc1 but I loaded this to see if it fixed the issue. Was also occurring on 7.2. Error 404 when accessing the web GUI, happens every week or so.

I let Claude have at this and it resolved the issue, but I can't speak for all of its logic. However, I did manage to get the web interface up again. After that, I ran diagnostics but I'm not sure what evidence it will have in it.

Claude's summary below of what it found and how it got the GUI running again.

Synptoms

• Web GUI returns 404

• SSH works fine

• diagnostics command exits silently with no output

• Array, Docker, and VMs keep running normally

• Syslog shows monitor cron failing every minute with exit status 255

Cause

The /usr/local/emhttp/webGui/ directory had been deleted from the /usr overlayfs (with lots of *- backup files left lying around in the plugins tree). PHP's auto-prepend file lives in webGui, so every PHP page failed to render → nginx serves 404/500. A reboot fixes access.

Fix (no reboot)

Mount the squashfs (/boot/bzmodules) to get pristine webGui files, copy them into the overlay's upper layer at /var/local/overlay/usr/local/emhttp/webGui/, then mount -o remount /usr so the kernel picks up the change.

unraid-diagnostics-20260501-0945.zip

OK the logic was flawed. I kept going and found the actual root cause.

I have some file backup trimming scripts that were still running on non-existent directories with poor logic. The directories didn't exist, and the file deletion runs in whatever directory cron is running from.

You can see where this is going.