Contact birthdays in calendar 404

Since the last updates on my nextcloud AIO instance, using DAVx on my android phone keeps showing
contact birthdays
http server error - HTTP 404

I tried toggling the switch off-on for the synchronization in DAVx to no avail.
Looking at the properties i see it is trying to find it @

mydomain.com/remote.php/dav/calendars/admin/contact_birthdays

while the Personal calendar works normally
mydomain.com/remote.php/dav/calendars/admin/personal

I remember trying to remove a specific birthday and future recurrences i am not interested anymore some days ago and since then the annoying message started popping up.

My server runs Nextcloud 27.1.5 on Docker (Nextcloud AIO)
PHP 8.1.26
pgsql 13.2.1
24GB RAM
Linux 5.4.0-169

DAVx5 Version 4.3.12.1-ose
Android 10 Google Pixel3XL

Any ideas?
Thank you