I have had this problem earlier. The requested temp was 375 F . Temp reached 375. A Pyrex dish with frozen burritos and refried beans was placed in the oven. I closed the oven door waited for the timer to start. Apparently, the temp dropped to 265 F when timer went off at 15 minutes later. The oven was turned off and back on. The temp came up to 375 F then held (took over 10 minutes).
Why isn’t the firmware seeing a low temp then increasing to preset temp. This seems to be a bug.
Reproducible? I have not tried to reproduce with the same results.