The OP doesn’t clearly indicate, but Hammerhead makes a proprietary mount for the K2 where the unit slides into the mount from the rear, not the quarter turn round mount as used by Garmin. HH provides an adapter for the K2 to use with Garmin quarter turn mount, that adapter installs on the device, which from what I read is what he is using on 3 of the 4 bikes, with the 4th bike using the Hammerhead mount. Possible the HH mount is causing the barometric sensor problem. I used to own a K2, was active in the Hammerhead FaceBook group and cannot recall anybody ever complaining about this kind of problem, but would suggest to the OP that he join that group and post this problem.