Health app steps reduces after a day

The past month I picked up that my Health app shows a specific step reading at the end of the day (for example 5 250 steps).

When I check that same days reading the following day, it reduced to a lower step count as was shown the night before (for example 4650 steps).

How is it possible to drop to a lower step count?

Example:

This screenshot was taken on 5 May at 09:05, showing 4 May’s step count as 5105:

This screenshot was taken at 19:34, also on 5 May - but the step count for 4 May dropped to 4923: