Xerath BUg

So i have been playing on the PBE for about a week now and have noticed that his ult will not go off and his passive will not proc on attacks sometimes. But when i play on the regular NA server I sill can't use his ult. I activate it and a the circle and a finger appears but I can't fire any of his bolts. It seems to be my laptop because I haven't seen it happen to anybody else and I have repaired and uninstalled league of legends multiple times. Any tips on how I can fix this?