I have the same problem.
Devices :
PC (Windows 10 May 2020) - Enpass Version : 6.41.642.0
Phone (Android 9.1) - Enpass Version : 6.4.2.337
Ipad Mini (9.3.5) - Enpass Version : 6.4.2
Every devices have Date & Time set on automatic (and are indeed on the same date & time)
When i first encountered this issue i already disconnected Sync on all devices, then deleted Enpass folder on OneDrive. Then re-Synced on all devices with the same vault password just fine...
It worked for 2 days it seems, and now i have the same error again : Sync Error - Password of data on Onedrive is required.