I would suggest trying the APC manually to see if the issue is caused by the APC's control circuits or a problem with the app itself.
Temperature can be manually selected by scrolling the wheel on the head of the APC, then press the 'play' button to set it preheating. Test with a vessel of water only, don't risk wasting any food. The machine will beep when it gets close to temperature. I would also use a standalone thermometer to confirm temperature if possible. Once temperature is reached keep the device running and check every 15 mins or so to see if temperature is holding.
If things check out ok with this test I'd suggest reinstalling the app as that is where the fault lies.
If the device fails the above test you will need to get in touch with Anova Support.