Roughly coincident with the recent 3.70 update, I find that my steps and stair counts are now being reset to zero at some point during the day, every day. The full counts remain in the sync'd Connect app, but the watch shows counts having restarted from zero at some point.
I would think your watch is crashing. It could be that you are using an IQ watchface, app, or data field that isn't 100% compatible with the new firmware. If does crash, the watch will probably vibrate and the display should show the Garmin triangle until it reboots.
That would be the first place I would look. If you are using an IQ watchface, I suggest you switch to a regular watchface for a day and see whether the behavior continues.
I don't know about a permanent resolution but one thing to try is to disable any CIQ Apps you may have installed just to see if they are the cause of the4 crashes. My CIQ watch face used to crash all the time but that was fixed with an update.
Got the same issue where 7 consecutive days my watch is deleting a minimum of 2k steps a day for no reason, nothing has been done my end and am really frustrated
