Zac E Releasing Early

I have been playing Zac and sometimes while using E it releases early. It has done it at the very start of the charge and sometimes halfway through. Each time the key is till being held down. I have tried with and without quick cast, no change. I have tried having mouse right next to Zac and further away towards end of cast range. Bug has occurred with both. Sometimes I can go 5-10 minutes without it occurring, othertimes it is one after another.