Ok... so I just rebooted my Unraid server and it came back up with a missing .M2 cache device! (I have a pair of 1TB .m2 mvne cards)
I shut it down completely and upon powering back up the device was rediscovered and now my smb shares are working fine from my Mac.
Very weird.
Attaching another diag' file in case it is of interest.
nas-diagnostics-20221111-1730.zip