Hello,
Thank you for reporting. I revert the fix as it was indeed the culprit and I din't find any other solution yet.
The next nightly should be ok, named sogo-5.9.1.20240214.

However, the events that disappear will not come back as they are still in your database, but with a startdate that has been shifted to the future, that's why you don't see it anymore.
You can either redo it or it's fixable with the database but a bit tricky. Let me know what you prefer.

Hello,

thank you for your fast response!

Getting the events back, was not a problem. I removed the reminders on my smartphone (Google calendar) and saved all occurences. After sync they show up in SOGo again. (If the start date was the problem, then Google calendar fixed it somehow...)

Have a nice day,
Timo