Hello,
I am currently updating from 11.0.7.3 to 12.0.5.3. Therefore I downloaded the latest12 from Index of /server/releases and followed the instructions on Upgrade Manually — Nextcloud 12 Server Administration Manual 12 documentation. 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