I run cadence / speed sensors on my MTB,CX and road rigs but I have noticed that at times the auto pause still kicks in even though I'm well above the 3mph limit I have set for auto pause. I assumed that given I'm using the Garmin speed / cadence senor the auto pause feature would default to what the speed sensor is reading but it seems as though the auto pause is still relying on GPS? I switched to the speed / cadence sensor given I often ride in heavily wooded areas and the GPS would drop out (along with also getting inaccurate mileage readings when riding tight switchbacks on my MTB). Does this sound right? It would seem reasonable that the auto pause feature would rely upon the speed sensor rather than GPS if you went to the trouble of purchasing and installing the speed / cadence sensor?

Anyone have any insights on this issue? Thanks.

Possible bad sensor. It happens.

Try replacing the sensor battery. They don't last all that long. Make sure the unit is pairing with the sensor before you move: start the unit and wait until it autopauses. Pick up the bike and spin the rear wheel. It should start and show a speed, then autopause when the wheel stops.

Yeah when your sensor dies it relies on GPS and then if you lose GPS reception your speed goes crazy (I have seen mine jump from 30mph to zero in the span of 2 seconds)

Most likely the battery, as others have said. Could also be the positioning of the sensor pick up. Probably should double check the alignment but you may have already done that.

You don't have a GoPro do you? Mine interferes with my Garmin causing the problem you're describing.

On outdoor rides, the Garmin uses GPS data to record the speed rather than the magnet (unless you've checked the 'don't use GPS' o.e. option in the settings).
*This was just my understanding of it when I asked a club-mate why my speed was 0mph on my rollers*

Thanks for the suggestions. I installed a new battery today. Hopefully that will resolve my problems. Cheers.