For more than 8 months, I have experienced intermittent sync issues with MisFit and I have communicated with their support team on numerous occasions.
My issue is always been related to a difference between the values displayed on the watch (Pebble Steel in my case) and the values stored on my account, either aligning or lower as if data had been missed.
My last communication with MisFit was a couple of weeks ago, and the status of any fix to sync issues was the same, "they are looking into it".
Given that; one, it is a free app, I doubt time and effort can be afforded in support; and two, with FitBit (their market rival) acquiring Pebble assets, the MisFit / Pebble association is probably doomed.
I like the watch app, and will continue to use it, but I have now abandoned the online sync facility with my MisFit account. It still happens, but I don;t bother looking at the results as I have lost faith in its reliability.
I now record the data off my watch manually. At 11:50pm, each night, I record the steps and points off the watch app and store it in a spreadsheet (at midnight it resets, so I have to capture it before then). In the spreadsheet, these values are tabulated by date where I can perform standard spreadsheet manipulations, like graphing the last 10 days of points, and I convert the steps into kilometres (distance).