Bosch Double Oven power dips during use

Hi Guys

My Mom has a problem with her 4yr old oven which I hope you can help with or advise.

It’s a Bosch Double Oven HBN56M0B.

The problem occurs with the top or bottom oven being used on any of the settings (fan assist, conventional, pizza etc.)

When the oven has been on for 20mins sometimes longer and gets up to the set temperature or nearly there the power blinks for a split second and the oven light flickers on/off and because the controls are digital the oven temperature setting defaults back to 100 degrees.

This causes a problem when my Mom is cooking or baking obviously because unless she has been checking the oven every 5 mins the food isn’t getting cooked at the correct temperature and the cakes aren’t very successful!

Its almost as if a relay on the board is breaking down and the contacts dropping off for a split second.

Anyone come across this before?
Thanks for any help
Nik.