hi,
Did you ever get a reply, I have the exact same problem with a new MARQ watch if I don't sync the watch before I put it on charge I loss the last period of steps, I have been making sure I do my 10k a day for 200 plus days and last week I know I did the steps, but forgot to sync the mobile (which was not with me) the following morning it recorded only 9000 even though I know I did more.. I'm 90% its when I split the mobile and watch and it's not sync before I put the watch on charge (circ. every 3-4 days).
While it might be a small bug it's very annoying.