I got a free replacement for my Medtronics Guardian 3 transmitter with a software update to prevent so many BG Required messages. When I first connected the transmitter, I was getting fairly erratic readings.
I cleaned off where the sensor plugs into the transmitter with some spray electrical contact cleaner, and then the transmitter started working normally. I didn’t actually spray this into the transmitter’s hole. I sprayed down the dummy plug that came with the original transmitter with contact cleaner, then inserted it a few times, sprayed it again, and inserted it a few more times. I was afraid if no-clean flux was used on the transmitter pcb when soldering the components, the contact cleaner could partially dissolve some of that no-clean flux and cause big problems with the sensitive analog sensor circutry. I’ve worked in electronics manufacturing, and have seen aggressive solvents used on pcbs with no-clean flux cause circuit problems.
I wanted to share this in case other people were having problems with erratic sensor readings. It could just be the connector where you plug in the sensor is dirty.