My rather large (iCloud) Comics Library has its comics stored in Alphabetical folders (A to Z), containing folders per writer (as artists tend to switch while most series have a definite “author/showrunner”, containing “series”, then “runs”, then individual comics. Graphic Novels are stored at the writer level. Multi-writer franchises (Marvel/DC/…) are stored in separate structures (but my main interest goes to limited, finished series anyhow).
I too have noticed the “greyed out thumbnails” bug.
As a partial solution and suggested feature, I’d like to propose a “lock thumbnail” option for folders. These thumbnails (Just as eg my custom “Alphabet” folders “A”, “B”, etc…) can “burn” their (temporary) thumbnail into a permanent “image” thumbnail.
This would have scanning/thumbnail creation skip these folders, and they also would no longer need to create an everchanging thumbnail whenever the contents switch.
As an example: my “REMENDER, Rick” folder, which now needs to check whatever folder(s) it contains, would sport the series I’d put front & center (eg “Fear Agent”) and create a thumbnail from this. If I were okay with a “Fear Agent” cover as representative of the “REMENDER, Rick” folder, I could then choose to “Lock the thumbnail”, and it would avoid thumbnails to be created, calculated, etc… at each new series I were to add to the “REMENDER, Rick” folder.
PS: Love the app, btw.