I recently noticed this when I updated a windows-based setup executable on a share, and all the sudden nobody could launch it. When I investigated, it seems that FreeNAS has begun manually specifying extra ACLs on created files.
For instance, in the shared directory I have a subdirectory with the permissions of "Everyone: Full Control, Domain Users: Full Control, Normal User: Full Control", that is inherited by all subfolders and files (and the foilder itself).
If I now create a file, said file gets "Special" permissions for Everyone, Domain Users, and the creating user of Read and Write, not inherited.
Noticed in FreeNAS-11.3-MASTER-201910231132, it's probably happened earlier and I haven't noticed, will have to sift through files and ACLs to see when this started happening...