I doubt that it really is freezing. More likely, it is doing something, but you can't see it. If you added two three lines at the very top of the Loop to turn a LED on, wait half a second, then turn the LED off, I bet it would continue to blink. More likely is that the thingspeak is returning for example the same relative value again and again. That gets interpreted to move to a specific Position. The move doesn't take place because that Position is already the current Position and everything starts all over again.