Problem is fixed in Github, either wait for the next maintenance release, probably end of the week, or run the following commands on your installation:
curl https://github.com/EGroupware/egroupware/commit/74713c652aa62448571758099ba065bd208cf010.patch | docker exec -i egroupware patch -p1 -d /usr/share/egroupware
docker exec -it egroupware kill -s USR2 1
If everything work, run the following to make sure the patch survives a restart of the container:
curl https://github.com/EGroupware/egroupware/commit/74713c652aa62448571758099ba065bd208cf010.patch | docker exec -i egroupware patch -p1 -d /usr/share/egroupware-sources
Ralf