Garmin's do strange things when you use them while stationary. Most want the gps disabled when you do stationary stuff. As for wheel and cadence sensors on a stationary bike, I'd hate to begin to guess. When I participated on the Garmin Community Forums many years ago, use of a GPS and sensors on a stationary bike or trainer seemed to have a lot of people having unexpected results.
You might check with them, the forum is still fairly active......
https://forums.garmin.com/sports-fit...ng-multisport/
https://forums.garmin.com/sports-fitness/cycling/