Hi Mike,
Most useful would be a log.smbd.exe with debuglevel of 3 and an attempt to connect from win10...
Here you are.
Greetings,
Mike
Here's the relevant part:
[2020/06/25 16:11:47.936000, 2] ../../libcli/auth/ntlm_check.c:429(ntlm_password_check)
ntlm_password_check: NTLMv1 passwords NOT PERMITTED for user Mike
[2020/06/25 16:11:47.936000, 3] ../../libcli/auth/ntlm_check.c:436(ntlm_password_check)
ntlm_password_check: NEITHER LanMan nor NT password supplied for user Mike
[2020/06/25 16:11:47.936000, 2] ../../source3/auth/auth.c:343(auth_check_ntlm_password)
check_ntlm_password: Authentication for user [Mike] -> [Mike] FAILED with error NT_STATUS_WRONG_PASSWORD, authoritative=1
As suspected, it looks like you've downgraded Win10 to use a lower grade authentication scheme to be compatible with older Samba versions...
NTLMv1 was disabled by default a few Samba versions ago. If you want to keep Win10 compatible with Samba 3.6, you can add (I think)
ntlm auth = yes
to the global section of your smb.conf
Of course, the better option for security would be to move 100% to Samba 4.x and fix Win10

Cheers,
Paul