Birthdays: some show up, some don't?!

Hello,
we have a shared address book and enter birthday dates via the date picker. Some of the birthdays show up in the birthday calendar, and some don’t. I can’t see a reason.

Any ideas? Any other info you need?

NC 22.2.3
Calendar 3.0.2
Contacts 4.0.7

You may be able to download the address book including all contacts into one file
If you open the file in the editor, you can see where the differences are in detail.
There may be differences between the contacts where it works and those where it does not.

Thanks for the idea. I looked at a few entries, here are the differences:

works:
all the examples I saw were VERSION:3.0
some were PRODID;VALUE=TEXT:-//Thunderbird.net/NONSGML Thunderbird CardBook V37.6//DE
some were PRODID:-//Sabre//Sabre VObject 4.1.6//EN

doesn’t work:
some were VERSION:4.0
some were VERSION:3.0
some were PRODID:-//Nextcloud Contacts v3.5.1
some were PRODID:-//Sabre//Sabre VObject 4.1.6//EN

The weird thing is that for the contacts whose birthdays don’t show up in calendar, it does not even help to change their birthday in the contacts webinterface nor in Thunderbird Cardbook. They just won’t show up.

Any ideas?

Any ideas what the problem could be, or what to try?

I created an issue, let’s continue over there Birthdays: some show up, some don’t · Issue #3914 · nextcloud/calendar · GitHub