Gas Oven Issue (Frigidaire; older model)

Preheated Gas Oven. Put two frozen meals in there, 35 mins later, meals were still frozen and oven had very little residual heat. You could touch inside without issue. When I put them in, the oven was preheated and hot. I went to watch TV and came back to oven off.

Tech installed a new igniter and it happened again. I came home last night and it preheated and didn’t turn off. The temperatures I had set it was doing this was 350° and 375°. I cooked a pizza AT 450° in between this issue happening and it came out perfect. Seems like the oven as an issue keeping consistent low heat.

Any suggestions? Tech thinks I am crazy and says the oven does
tend to go into a passive mode to keep consistent low heat but how does that explain the frozen food still being frozen after a half hour.

Google said could be sensor issue and/or control board. Any suggestions would be nice. Thanks