[Samba] system error 58 when guest connects from Win10

[Klaus Hartnegg]

I cannot connect as guest from Win10 to Samba anymore,
since I removed "server max protocol = NT1"


   net use \\%IP%\testshare /user:"" "" /persistent:no

   System error 58 has occurred.
   The specified server cannot perform the requested operation.


It works when I supply a userid and password.
It works from Win7.
It fails only in the combination Win10, SMB3, guest user.

Samba is version 4.5.8

smb.conf has these lines:
   server role = classic primary domain controller
   guest account = gast
   map to guest  = bad user

This is the share declaration:
[testshare]
     path = /srv/samba/files/archiv
     guest ok = yes
     read only = yes
     locking = no
     admin users = +smbadmin

The option "smb encrypt = off" does not help.
The option "server max protocol = SMB2_10" makes it worse.

A similar issue is described in
https://lists.samba.org/archive/samba/2016-August/201876.html
https://bugzilla.samba.org/show_bug.cgi?id=12136
but that cites WinPE, not Windows 10.

Does smb signing require a userid?