Calendar stops generating in October

Hi together,
big issue with our instance of Libretime.
The Calendar stopped generating on the last day of this september.
Trying to access the calendar in “Month” view fails with a 504 Timeout.
The API just shows this week with content, starting next week it stops and has no content.

I had this once and was only able to recover with a fresh install, even backing up the DB and Audio etc. and importing to a new host did not change the problem.

I have no clue where to start searching for this, i’m totally lost.

Currently running on Version 4.0.0 (updating is hard since the Instance is feeding our FM/DAB+ Station, downtime is a no-no even for a few minutes.
Base System is Debian 11, Libretime was installed with the installer script.

If anyone knows how we may get this instance repaired without setting up out Database from scratch i would be happy to know.

Greetings, Chris