One particular user in organization looses groups

We have a weird issue with one user in our organization. We use a self-hosted docker-based bitwarden instance

bitwarden.sh version 2024.7.2
Docker version 27.1.1, build 6312585
docker-compose version 1.29.2, build unknown

our users are LDAP based and are synced regularly with bwdc via a cronjob. Only one particular user has the problem that his group-bindings (also from LDAP) get lost every then and when. I assigned him at least three times already to the respective groups but latest after two or three days he comes back to me telling that he cannot see anything in the password manager anymore. Then when I login to our bitwarden instance I can see that no group is assigned to his user anymore. We have about 30 users in our organization and he is the only one that has this problem. I already tried to delete and re-create his user but again after two or three days the groups are gone.

Does anyone have an idea what that problem could be?

Thanks a lot for any hint and have a good one

tobi