The Client Disappears

This has happened to me multiple times and it is quite annoying.Basicly the clients just vanishes.I don't know what triggers the bug ,but it has happened when i start a game, when i got to the hextech crafting menu, when i try to recconect to a game or when i got to the store.The weird thing is that when i start it gives me that error "Another instance of the client is running.Do you want to terminate it ?" so that means that the client is still there but it's invisible or something.

EDIT:It doesn't happen often but i still think it has to be checked out.