That connection is in a bad place. You have it set up to connect each time you pause or resume the game. But if you connect multiple times, your slot will be called multiple tiles for each signal emission.
Make sure you only create the timer and connect to it once. I suggest moving the timer construction and signal connection into your GLWidget's constructor. Store a pointer to the timer as a member variable of your class so you can start and stop it in the class's member functions.