Mario77 CIFS (OS) mounts will (in pre-4.13 kernels*) default to SMB1, so yes your SMB1 CIFS mounts will fail when connecting to an 8.1.1 Samba server using the default SMB2 min protocol setting.
Your options are to enable SMB1 on the LE 8.1.1 Samba server (not a good idea), or add "vers=2.1" (or better) to your CIFS mount service in order to establish an SMB2 (or better) connection, ie.:
Code# Any options you usually use with the "-o" parameter in the mount command Options=username=USERNAME,password=PASSWORD,vers=2.1
Adding "vers=2.1" to the service may already work when connecting to an older LE 8.x or 7.x server, so could be added before any server upgrade.
We may need to update the sample config/wiki to mention the vers=x.y option.
* starting with 4.13.0 the kernel will now default to SMB3 when establishing a CIFS mount.
This makes a lot of sense..thanks milhouse