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 @

while the Personal calendar works normally

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
Linux 5.4.0-169

DAVx5 Version
Android 10 Google Pixel3XL

Any ideas?
Thank you