Well... I made it to work...

I disabled my antivirus (TrendMicro) and SQL instantly started working normally.

Then I enabled the antivirus back and SQL was slow again.

I...

Initial Login to servers is not affected by this lag - after login when SQL starts to connect to databases (next to server name in brackets with 'expanding...') The same...

I have SSMS RELEASE 2016.5 installed. Tried reopen/reinastall - I even did format & reinstall Windows 10 (with like 1 month of great SQL working connections)

I have no options...