Cannot upload or edit files on Seahub after upgrade vom V11 to V12

Hello,
I just recently tried to update my seafile server from V11 to V12.
To be on the safe side, I first did a test-run, setup a new V11 in a VM and upgraded that to V12 by simply changing the image tag in the docker compose file (as I don’t need seadoc or the new caddy-docker-proxy).
That work perfect, seafile upgrades and I can use it as before.

However, with my production system, I cannot upload or edit any files in seahub. Interestingly, I can delete files in seahub. And via the official clients, everything works as before.
What’s going on here? How can I fix this? Or investigate the issue further?
Of note, I’ve been using caddy (not caddy docker proxy) for a long time as my main reverse proxy, this connext to the seafile container on port 3001 as seafile is exposing at that port the internal port 80…

Thanks for any advice that might help to get my system upgraded!
Kind regards,
Ruediger
P.S. After downgrading, functionality in seahub is restored.

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