mSecure 6 overwrote newer records on sync and lost data.
Thank you for contacting us, and very nice job with your analysis! You nailed exactly what happened, as the Windows version that is currently in the available in the Microsoft Store is updating the modification date after the upgrade. This behavior will be fixed in the nest release we plan to submit as soon as possible.
Thank you very much for your time, and please let us know should you need further assistance.