Temperature Swooping Up and Down

Hi all. I just started using my APO a few days ago and love it. But today something happened I haven’t seen before. I tried to follow the “Omelet 101” instructions. I started the oven and its first job was to preheat to 181 F. It slowly climbed up, up, up to around 177 or so, then suddenly started declining to around 141. Then it started climbing up again, but again swooped back down after reaching the upper 170s. After a third round of this, I stopped the oven and tried to see if it made any difference if I set the temperature manually. Nope. Ultimately my omelet came out, after 20 minutes at wildly divergent temperatures, and it was OK, but I am not happy that the oven didn’t just hit 181 and stay there for the five minutes it should have taken for the eggs to set. Anyone have any ideas? Thanks in advance.