sui_scoreboard seems to be causing Garry’s Mod to freeze temporarily when opening a menu (Q, C…). Any server that uses sui_scoreboard has this problem. Remember though that the scoreboard is just a module for ULX. ULX on it’s own does not cause any issues for me.
This started happening after the update that Valve published on June 27th. I’m positive that the problem is sui_scoreboard since all issues disappear when you remove the addon from your server. If you’re a server owner please test this yourself by removing the scoreboard from your addons.
Hope this helps!