PHP error on invalid UTCDateTime compatibility

Hello,

in addition to the other WEBDAV error with invalid SQL i see a lot of the following error messages about some incompatible types.
The uuid of the vcf file differs, it seems there are maybe half a dozen ones affected.

2024/01/19 15:21:04 [error] 25#25: *3073 FastCGI sent in stderr: "PHP message:
PHP Fatal error:  Declaration of EGroupware\Api\Contacts\JsContact::UTCDateTime($date) must be compatible with EGroupware\Api\CalDAV\JsBase::UTCDateTime($date, bool $user = false) in /usr/share/egroupware/api/src/Contacts/JsContact.php on line 1077" while reading response header from upstream,
client: 172.21.0.1,
server: _,
request: "PUT /egroupware/groupdav.php/stefan/addressbook/eb63f5d8-5aef-4f38-a360-7123184dd20e.vcf HTTP/1.1",
upstream: "fastcgi://172.21.0.4:9000", host: "xxx"

Debian server, EGroupware installed via DEB packages running in Docker containers.
The client might be either Thunderbird 115.6 or latest DAVx5 4.3.12.1 on Android. I do not know because there are so many error messages.

$ apt show egroupware-docker
Package: egroupware-docker
Version: 23.1.20230314-1

# apt show base-files
Package: base-files
Version: 11.1+deb11u8

What might be the problem here? Some things to do to shed more light on it?

Best regards,
Stefan