LDAP/AD user cannot share the files

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Nextcloud version (eg, 20.0.5): 18.0.14
Operating system and version (eg, Ubuntu 20.04): ubuntu 18.04
Apache or nginx version (eg, Apache 2.4.25): apache2
PHP version (eg, 7.4): php7.2

Is this the first time you’ve seen this error? _(Y/N)_Y:

nextcloud integrates LDAP/AD users, and sync AD users and user groups,
When a folder is shared to a user group, all users in the user group can synchronize the folder normally,
but when a new user is added to the group, the user cannot synchronize the folder.
I donot know why , there is no error infomation.

E.g:
user A and B are belong to group IT_Group , and share the folder test_files to IT_Group.
So both A and B can sync test_files normally.
Now I have a new userC who joins the IT_Group group, but he cannot sync test_files. it must be shared with user C again before sync can be achieved.
Is this operation normail ?

I think the folder has been shared to the group, and all users in that group should be able to share it, regardless of whether the user joins first or joins later.

is there someone help me ?