If you reinstall from .msi of 2.0.6.3, that should make the base version 2.0.6.3, so should work with DB.
Are you running Duplicati as a Windows Service? You’d have had to run Duplicati.WindowsService.exe
That was the first test. Duplicati checks file contents too. You can now see if any files have newer dates.
There is a procedure for a more thorough check in the topic I cited earlier, or see the bottom of this post.
Did you confirm that BaseVersionName is 2.0.5.1? You can still go back to that with an .msi install, if you would be willing to look at the problem further. For example you can move the old 2.0.6.3 update to some other folder, try another update from 2.0.5.1 (you might need to start Duplicati to actually get it activated)., then see if About on home screen says 2.0.6.3. About → System info ServerVersionName will also say.
If it got to 2.0.6.3 then the question is how is this 2.0.6.3 update different from the other. You can compare folders carefully or even swap them around by hand. If one works and one doesn’t then find the difference.