MEATER probes can not be used in a microwave as this causes irreparable damage to the circuitry inside the probe, and is a fire hazard.
On top of this, Bluetooth operates on the same frequency band as microwaves, and because microwave doors are built to keep harmful waves from getting out, this also blocks Bluetooth signals. This means that combination oven doors can prevent MEATER probes from connecting, even if you aren't using the microwave function.