[Samba] Samba log flooded with 'guest user not permitted to access...'

[BW]

I've been struggle to find the source of a lot of error-messages in the
client-related samba logs:
  create_connection_session_info: guest user (from session setup) not
permitted to access this share (DATA)
  create_connection_session_info failed: NT_STATUS_ACCESS_DENIED

The users are successfully authenticated with their own username and can
access the shares without problems, but still Win10 seem to keep trying to
access the share as guest behind the scene.

And now I finally found the source: Windows defender, Real-time protection!
If I disable it I don't see these error. I've tried to add the server and
mapped network drive to the Exclusions list, but it doesn't help.

I am running the samba server in standalone mode (no domain). Maybe
defender will act differently in a domain setup.