My server had a major lag spike and i some players can't connect to server anymore,  they getting error: Invalid packet: client ready
I tried to restart, update.. but still the same.

Also added screenshot from console when trying to connect to server

Have you restarted the server?

Yes and i did update couple times. It's not for every player, but there are players who can't connect.

"in-depth" Google research says this was a big issue a couple years ago. I don't have a solution but I have a drastic idea (along the lines of fixing the RPC client errors, etc):

Full wipe with all the server identity .db files??