I don't look at this page much, but did today and see it looks weird.
Using the Steps widget and entering full screen mode for the widget to see the step history I note a weird chart. It seems to show my steps went up to ~18k then dropped to closer to 10k and settled there. I think this occurred during or around a run that I did. The run had GPS and an HRM Pro+ connected.
I wonder if it somehow added double steps from the HRM and the watch (?) but then properly removed the duplicate steps? It's odd, as, steps shouldn't decrease during the day, right?