Sync-Problems with Nextcloud Client 3.0.1 and below

Dear Community

I am having a Nextcloud Problem no one is able to solve.

The client works fine, unless you are 3 levels deep i a folder structure. If I upload a new file in lvl3, it is only me who sees the file via Nextcloud Client. It works without Problems via Web-Access. If other persons want so see said file via client, they must uncheck the sync-box and than check it again. Then it sees the “changes” and download the new file aswell.

Nextcloud: 18.0.6
Client: 3.0.1 as well with all other versions so far…
External Storage: Windows Server 2016


Has no one else the same issues?