Frigidaire wall Oven fails in Convection mode

Model Number: GLEB27S7CBB
Brand: Frigidaire
Age: More than 10 years

My Frigidaire GLEB27S7CBB wall oven stops heating after a variable number of minutes when in convection mode. It holds temperature and works for hours in bake, but is not reliable in convection. The fan is running and the display shows the set point, but the temperature drops. I have replaced all relays on the control board, but it is the same. I have not checked the broil element or temperature sensor yet.

Sounds like a control board problem to me.

The odds are high that the oven sensor is OK as the unit works properly in bake.

Same applies to the broil element though I am 100% sure about this.
Most units switch back and forth between bake and broil during pre-heat and the bake cycles so I would think that a bad broil element would also affect the bake cycle.