This mean in v8.1.1 C2 connected with SMBv1 protocol but in V8.1.2 samba was updated and not accept connections until protocol version is added to Options field?
Partly correct, as it's not really a Samba issue (at least, not in LibreELEC) it's a kernel issue. With 8.1.2 the kernel now establishes CIFS vers=2.1 (aka SMB2) connections by default, whereas with older releases (8.1.1 etc.) the kernel will establish CIFS vers=1.0 (aka SMB1) connections by default.
With more Samba servers dropping support for SMB1 (and security conscious users disabling it) the kernel developers recently made the decision to stop establishing CIFS vers=1.0 connections by default.
Most LE 8.1.2 users won't notice this change, it's only going to affect users with older Samba servers that don't support SMB2 (or are not configured to support it, which is probably the case with your server as Samba 3.6.25 is capable of supporting the SMB2 protocol).
Try adding the following to your Samba 3.6.25 server config, this will disable SMB1 but enable SMB2:
Given the age of your server you should also consider an upgrade, as it's not secure.