A couple of days ago I installed the latest Windows 10 version - 1803.
The following problem manifested itself immediately after install:
Whereas before the update I was able to see the thumbnails of the PDF files stored only on One Drive (not locally) in DOpus after the update I cannot.
In order to get thumbnails now, I have to store the One Drive PDFs locally. If I select a few of the PDFs in my One Drive PDF folder and tell One Drive to "Save space" by deleting the local copies, the next time I open Opus those thumbnails have disappeared, but the locally stored ones remain.
Obviously when I call those PDF files back to my local disk the thumbs re-appear.
I have done absolutely nothing viz-a-viz One Drive before or after the upgrade.
Looks like Microsoft have been "improving" Windows 10 again. After all they have restored the registry entries that deletes thumbnail cache automatically at boringly regular intervals.