Server lag on player join/disconnect

I own a TTT server and it has lag spikes every time a player join or disconnect (around 1 or 2 seconds).
It happens when I change the usergroup of a player too, so I think it could be related to ulib and ulx (I am using the latest version of both).

The problem started around the last gmod update.

Mine did this all the time too. Was very annoying. What addons are you using?