I can't access my Nextcloud

Hope someone can help.

This is Nextcloud snap on debian on a raspberry pi

Yesterday, all was well. Today I find I don’t have access to my nextcloud. It says maintainence mode. Later, I can’t access even that. ‘Unable to connect’
I can SSH into the pi and trying to start Nextcloud tells me it’s in a refresh cycle. Well, it seems to taking an awful long time about it.

Any ideas?

Edit

A little clarity. It’s a Pi4 and it’s running Raspberry Pi’s own debian (PiOs?) based on deb bullseye and the snap is the current stable version. I’m not sure what that is, but 27 seems to be in my head.