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.
I have been able to recreate this problem. I preheat the oven to 400 F. I fill a baking dish with ice. I open the door and insert the baking dish. The temp reading on the handle starts decreasing. In 14 minutes the temp is at 280. It continues to fall at a slower rate over 1 hour 26 minutes. I then change target temp a few degrees 400 to 396 F. The temp starts moving up reaches new target temp in 24-25 minutes. It doesn’t recover after the cold dish is inserted.
I was advised by support to unplug the oven and plug it back in. I waited 30 mins. The firm ware level did not change. The problem went away. Support did not provide any reason for the reset, Maybe there was a reload of firm ware … Something possibly was overlaid in the firmware or some hardware glitch changed the firmware.