The recently released 1903 update for Windows 10 introduced a number of problems with OneDrive support. To work around these Opus 12.15 and above disables some functionality when working with OneDrive. As these problems appear to be of a random nature we have added a registry patch flag that you can use to turn this functionality back on if you want to give it a try.
Hopefully Microsoft will fix these problems in their next update but on their current trajectory of releasing major updates without any real testing it seems unlikely!
The registry key is HKEY_CURRENT_USER\Software\GPSoftware\Directory Opus (you can also set this under HKEY_LOCAL_MACHINE to make the change for all users on the system).
Add a DWORD value called OneDriveBugMitigation. If its value is set to 0 then all bug mitigation is disabled and OneDrive functionality will be fully restored (although obviously it may not actually work properly). You can also combine the following flag values to selectively enable some aspects of the mitigation:
For example, to enable thumbnails but leave the other problematic functions disabled you would set OneDriveBugMitigation to 6 (2 + 4).
Note that you need to restart Opus fully for changes to this value to be noticed.