[XODIDOX]

@ashlar, movie version and movie set are totally different, though they look like similar in some ways. Movie set item itself is virtual and is generated on the fly, but all items in the movie set are real items, they are in video database, each one has separate entry, and Kodi is designed to work with them natively. In contrast, all movie versions under a movie item are virtual and are generated on the fly, they shared the same entry in video database. The movie item itself is in video database. If you checked the "as folder" option, the movie version item itself is virtual too.

Each time you are entering (or returning to) a media folder, the list will be refreshed, and Kodi will recreate these virtual items. The perf problem seems to be due to the additional database access for video version information query (if you uncheck the "as folder" option, no database access at all), I'll see if I can optimize the additional database access. You have many items in the list, right? It may help me debug the problem if you can share the debug log.

For the artworks, I designed a new media type for the movie version, so each movie version can have different artworks. I may be able to use the artworks from the movie item itself if the artworks for the movie version are empty, to "improve" user experience (I didn't add this as I thought using same artworks for all items in a folder looks boring).