Please go to /dopusdata and then zip up the Collections folder below it, in case we need to look at what was in it (or you have collections that you want to restore after testing).
Then, open the same location in Windows Explorer, and fully exit Opus using File -> Exit Directory Opus to ensure it is not running in the background.
In Explorer, delete anything that was in the Collections folder (but leave the folder itself).
Restart Opus.
Do you still see the same problem?
If you no longer see the problem, please send me the zipped collections folder made earlier so we can take a look at what might have been causing the issue.
If you want to restore your collections, fully exit Opus again, unzip the collections folder (using something other than Opus, of course), then restart Opus.