Hello,
I am currently updating from 11.0.7.3 to 12.0.5.3. Therefore I downloaded the latest12 from https://download.nextcloud.com/server/releases/ and followed the instructions on https://docs.nextcloud.com/server/12/admin_manual/maintenance/manual_upgrade.html. The update up to call of occ was successful. I loged in as user and I could not see my contacts. Instead I see the attached screen.
If I search for contacts it works and after I used Firefox instead of Chrome also the list of contacts was working…
bests
Sascha