OH3 UI wont start after cleaning cache

I was trobleshooting a problem described in this post

But after cleaning the cache, openhab UI will not start.
I’ve rebooted about 4 times now.
My other software, Plex, PiHole etc are running fine.

No automations are running and switches and bulbs etc aren’t triggering anything.

Can’t log into openhab-cli console. I get the error ‘Failed to get the session.’

openhab-cli status shows openHAB is running with PID: 906 and has been running for 03:57

OpenHAB version 3.1.0.M3

Sounds like -

Not sure.

I just downgraded to stable release, then back to Milestone release and everything seems back to normal.