I would remove the belt and hand check everything. Total speculation, but maybe you have a bearing that is seizing up or worn out? Something is locking up the belt and not allowing it to turn, makes sense that you should be able to feel an issue if you wiggled them all by hand to see what kind of play you have or if one does not want to turn freely (The ones you can turn without engine on, like the water pump). May even be worth having someone start the engine briefly while you are back there to see if anything is not looking right, or making weird noises. Perhaps you will find your issue that way. Good luck.