Indoor Distance way off!

My new Venu3 is WAAAAY off on calculation of distance for indoor walks. I know I should expect some inaccuracies but not a factor of 5. I did a 4 km walk roughly 5000 steps) on the treadmill & the watch indicated 0.9 km. Garmin suggested that I do a treadmill calibration, but that requires that the watch record at least 2.5 km; which means that I'd have to walk about 10 REAL km for the watch to read that. I already did a total reset of the watch but it didn't make any difference.

Any ideas?