azche24

Two things turned out to be crucial for this sort of errors:
Unraid comes with an inferior samba implementation (at least in my user-experience): No home directories, no consistent user-management in the gui including the smb aspects and no proper rights management for new created files/directories (see following #2). Every time a known and validated user (like me with my user-account without any  @ in the user-name) writes to the shares, creates files or directories the given user-rights get shaken up. This happens no matter if you go over a web interface (like creating or renaming files via filebot docker web interface) or directly from windows via file managers. So i googeled this stuff and the only fix or workaround is to add something to the smb-extra.conf in the flash-drive /config directory:  
logging = 0 force create mode = 0666 force directory mode = 0777 force user = nobody force group = users create mask = 0666  
Then hopefully every single file or directory you create like in step 1 gets the right file-mask/permissions. Otherwise you have to re-write them via "Docker Safe New Permissions" very often (which is a pain in the a..).
 
I never ever had these kind of quirky samba experience with any fileserver or nas OS i was using in the last 20+ years. OMV, TrueNAS, Koozali, Synology, Qnap - you name it. Only unraid does this kind of quirks - the main reason i would never ever trust it in a multi user windows centric environment.
 
So these additions to smb.conf don't make it flawless. But it is a start.