after further trial/error, I found out that I can create successfully a new accessible NFS/Samba share folder created on HDD "A" for example, but if I create a folder on another HDD "B", then this folder is not accessible via the Samba share. This doesn't make any sense to me as I can see that the permissions, user:group are set to exactly the same way on the HDD side, the NFS and Samba permissions.
For clarification, my HDD "A" is an HDD with existing shared folders, which all work fine
my HDD "B" is a manual replacement of a faulty HDD. I manually removed (via the OMV interface) previous shared folders, NFS/SAMBE shares and created new ones mapping this new HDD. I had done this in the past without any issues. But this time, this hasn't worked as said in my first post