This is starting to sound like a short somewhere in the electrical system. If sometimes it will advance on the timed cycle and sometimes it won't.
If this is the case then you might want to check for chewed or broken wires.

Hi I just fixed my dryer today. I have experienced the same symtoms as you. There is nothing wrong with your timer. It just stop advancing becuz your cloths is not drying properly. There is a sensor that senses moisture in the dryer. The timer will proceed if the clothes are drying properly. Your clothes are not drying properly is becuz
you have no heat. You only have heat at the beggining but not after 10 min. So your clothes is not drying right,
with much moister the sensor detects, so it stops the timer until the moisture level drops. I changed out the
gas valve coils and is working great. I have wasted money on changing out
the sensors and still had the same problem. It took me
another week for the gas valve coils to arrive. I was so thrilled that my dryer is working right again that it makes me want to share this info.