Ok so hear me out, please ...
I've had unRAID only since 6.x and only use NFS. No SMB. I've experienced, many times, the issue where all /mnt/user shares completely disappear (from a mount perspective - the data is still on the disks). Rebooting solves the issue each time.
drwxrwxrwx 2 root root 40 Jan 27 14:51 disks/
d????????? ? ? ? ? ? user/
drwxrwxrwx 1 nobody users 174 Jan 30 12:58 user0/
Note that /mnt/user0 still has the exp