Wow, that's a problem, that downspike totally looks like what happens when you open the hood. I bet that Meater is damaged. I just really, really cleaned the ambient end with a green scrubby because it wasn't making good contact with the charger, and it solved my problem which was losing contact with the phone app a lot. I guess it was acting weird because it wasn't fully charging. I scrubbed the heck out of the end and all of it actually, so that there was no brown residue anywhere, then dried it off and charged it and it is back to normal now.TH, I don't trust the ambient sensor in my MEATER...here's a graph of my last cook (keep in mind that I didn't open the lid the entire time, only when the MEATER said it was done).
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Other cooks show a similar pattern. The ambient sensor and my Smoke ambient disagree by as much as 40F. Of course, my MEATER may be damaged, but may I suggest that you check your MEATER ambient against another ambient before you rely on what the MEATER is telling you?
If I were you, I'd give that Meater a good scrub even with some brillo and then charge it up and see what happens.
I only have a Meater, no other fancy thermometer. Of course, I do have an old school meat thermometer but it does not charge or is not cool in any way except that it works as far as I know, so I do have a backup!
The birds have been coming out pretty good, and I think if the Meater totally failed at this point I'd be able to gauge when a chicken was done.
Your ambient temp graph, I see that big down spike, but did you also lower the temp at the end of the cook? Looks to me, judging by the internal temp, you did not. Your ambient seems really off, do you trust the internal temp?