Though ULX does have a few hooks that watches PlayerDeath, we don't modify the AddFrags function or variable, ever, to my knowledge.
It would seem my original belief it's a conflict of TTT code.
Looks like somewhere in TTT, PlayerDeath is returning something that breaks other addons (including ULX in this case), and causes the game to hang because that's how a game usually ends, when a last player dies.
No Gmod function should return anything unless the author REALLY knows what they are doing.
I'm not saying for 100% sure it's not our fault.
I'm just 98% sure it's not our fault.