Group folder - user lost write authorization


I had a group folder on wich a group A had write and share and group B only view authorization.
it has been working for a few month and suddenly users from group A don’t have anymore write access.
all my users are ldap, i’ve tried with ldap or local group.
i’ve also tried to deleted and recreate the group with no result.

do you have any ideas before my users begin to share on their side?

Nextcloud version (eg, 10.0.2): 12.0.0
Operating system and version (eg, Ubuntu 16.04):ubuntu 16.04
Apache or nginx version (eg, Apache 2.4.25): apache 2

Is this the first time you’ve seen this error?: