My cs resets everytime when i play with Gangplank

Everytime when i play my cs resets .EX : Last match i had 291 cs and then it showed to me that i ve got 200 or something like that.this thing didnt happen to me once, it happened for about 5 times in the same match .Idk if it is only for , and idk if it just happens to me but i want some explanations