High limit temp sensor

The first place to start is with the convection blower, clean it and pay attention to the motor and its cooling fan they need to be kept clean as well, then oil the blower motor if it is an oil able motor the makers plate should tell you if it is and what oil to use. They frequently need oiling every six months. Sometimes the oil ports are pointing down and that should be corrected if possible.

How old of stove? Cleaned and oiled the fans lately? Without a accurate temperature gauge or IR gun its hard to check the snap.

I was making general questions on the service of the stove. You may well have your fans bearings going. Five years without its annual oil may have sealed its fate prematurally. Maybe someone with more knowledge on your stove model will join in. Maybe the fans bearings can be replaced?
Good luck

When was the last time the exhaust pathways were cleaned? Also the exhaust pipe its self? You need to look in all areas that can/could slow down the exhaust gases. The snap disc could just be bad also. Have you ever had to reset it if its a resetable one? The bearings going bad could cause the rpm's to drop enough on the fan to cause the temps to rise enough to trip the disc. I'm thinking your bearing are shot and need to be replaced mainly because you asked about increasing your CFM, and yes, I know that may just be something else you would like addressed.

I would clean the stove/exhaust if it hasn't been done recently.
Replace the snap disc.
Replace the bearings or motor.

I feel that if you do the above you will have covered all bases. Others will chime ion if I've forgotten something which I'm sure I have.

I don't think a failing combustion fan-motor would cause the high limit switch to trip as the exaust is not flowing it would be getting cooler if the convection fan is doing its job and extracting the heat. Combustion fan is probably due to get pulled and cleaned properly. Most models will need a new gasket after removing the fan unit though. I am surprized no one with this model of stove has chimed in.

What trips the sensor assuming the sensor is good is insufficient air flow to keep the heat exchanger's temperature below the trip point.

There are two air flows that count the convection air flow which removes heat from the exchanger and dumps it in the room a dirty or failing or unmaintained convection blower is the leading cause of high limit trips provided the stove is not overfeeding pellets (improper feed gate setting if any, burning other than approved fuel, incorrect auger motor replacement, etc ...)

Then there is the combustion air flow here the primary culprits are a dirty exhaust system, a failing combustion blower, or an improperly installed vent system.

It is possible for both air flows to contribute to the sensor tripping.

The high limit sensor I'd trust.