Freezed client - help

HI Riot! In the game while i should pick champion sometimes client freeze and i CANT click anything, counter in the middle of screen (time left to play) is "freezed" too, only think i can do then its typing on the chat. Im loosing LP beacsue of that. I lost PROMOTION GAME not once beacuse of that. Sorry for big lettering but im little annoyed, i send similiar delating but got no answer. Im stucked in silver beacuse of that for a months...