Thresh attack is not smooth

IN S5 Preseason, i trying use thresh to jungle, and i focus to build Attack Speed as thresh passive given him a lot of additional dmg after attack people, just like a adc.

The problem is that Thresh Attack speed beyond 2.0, his attack is not smooth, sometime thresh stop his attack and stay here, nothing to do. This problem i found it out on Tai Wan lol version, as my account transfer to Tw server, my account data is gone, thus i m not sure that na server cause this problem too. But i thought it may cause Na Server too.