One of 5 NFS-Shares will not be shown in the UI (External Storage)

Hello experts!
I’ve five NFS-Shares on my NAS (Video, Music, Pictures, Share, Scan).
This shares are mounted in Nextcloud via External Storage.
All shares are visible and accessible in the OS.
One share (Pictures) will noit be displayed in the Nextcloud UI.
Any ideas? Recommendations where to look?
Nothing to see in nextcloud.log.

OS: Ubuntu Server 18.04 LTS
NC: 15.0.0

Kind regards EU