Steps just disappeared overnight

Last night I looked at the app and saw I had over 9,500 steps, so I did 500-ish steps and got the 10,000 step notification, yay! I did a few more just to be safe, then went on to bed.

This morning I look at the app, scroll it to yesterday to enjoy my 10k victory, and see... 9,266 steps. What?! Why?? :-(

And don't even get me started on the hourly step goals...