What causes repeat trip of thermostat in dryer?
The most probable cause of your dryer over heating is caused by a blockage of air flow in the dryer exhaust venting. This has happened to me and causes the dryer to display a flashing AF (air flow) indicator. 

Blockage is generally caused by build up of lint in the venting duct. It can also be due to something closing off the outside end of the vending duct such as snow buildup or or the vent flapper door getting stuck shut.

In my case there is about 22 feet of 4" ducting that unfortunately has to route through seven separate right angle joints as the duct goes up through an inside wall to between floor joints between 1st and 2nd floor before it finally makes it way through the back garage wall to the exterior. Even though the dryer has a good lint screen that is cleaned regularly some lint makes its way out with the warm damp air into the duct. The long duct cools the air and allows a good share of the lint to end up sticking to the inside of the pipe. Eventually over time the duct work needs to be opened up and cleaned....a painful and lengthy job.