Import from WoltLab Calendar

[Frozen_byte]

AppVersion: 1.5.4 (fdroid)
Android: 8.0.0
Model: One Plus 3

I added this link to sync: https://operation-pandora.com/calendar/index.php?calendar-export/13/&at=56-aae10ba16840c33e2d63a6486e061e1b1c5d929d
Calendar was added but no event was created.

Any suggestions?

[rfc2822]

Hello,
I have tried and it works here without problems.

Do you get an error message?

[Frozen_byte]

update: The export from WoltLab is wrong; the last Event in the ical file is 16. May.
I guess this is caused by the "Sub-Categories" in Woltlab. I had to export each sub-category by its own to get it working.
Thank you for your help, this issue is solved.

Sadly, there is no error by manual sync. Is there any logfile written by the app I may provide?

Already tried to wipe data and reinstalled from F-Droid store.
Here are some random images that may give you more information.
Seriously, I have no clue what is wrong: