Django reports "Bad Request 400" After Migration to Raspberry Pi

During the last days, I have tried to migrate my X86 Ubuntu-based Seafile Community Version on 8.0.7 to a Raspberry Pi with the same version.
I succeeded in getting it running and moving the database, but when trying to download single PDF documents, I got a “bad request” (in set password) and some “suspicious event” logged by Django in the seahub log. I wasn’t able to download the document from the web page, but for a simple text document it worked fine! The libraries are encrypted.
Has anybody an idea what could be wrong? I have replicated exactly the same NGINX configuration, and everything else seems to be 1:1 (Ubuntu 20.04). Maybe I have forgotten to copy one of the config files, but so far it looks quite similar.

django.request:222 log_response Bad Request: /api/v2.1/repos/


I have slightly changed the gunicorn config but this shouldn’t have been an issue. After deleting all cookies, it worked like a charm.