There are two numbers showing in my activity, one is the correct number with the correct time frame, 12:00 am - current time , the second number starts at 12:00 am -11:45am.
Could you give us a screenshot so we can better spot the problem?
From what we have tested, it may because Fitbit give us cumulative number of steps, how much steps does it show on Fitbit app?
The bottom number reflects the number on my Fitbit. This does not happen everyday, but more days than not.
I tested out your theory. Yesterday I did not sink until the end of the day. I checked and made sure my steps for the day were 0,then synced with my Fitbit. As you can see there are 2 separated step counts which have been added together. The correct step count is 2038. This could be a fun and motivational game, too bad you can’t get the step count issue resolved.