[pkscout]

As for the featured artists not showing, there is an error in the log about a file that couldn't be deleted in the merge directory. Could you check and see if user_data/addon_data/script.artistslideshow/merge is empty? If not, delete the merge directory and let AS recreated a new one. Maybe that will help.

While doing so I found that in this folder all fanart is correctly merged however not all of them are displayed.

Log 

Unfortunately there's nothing I can do specifically about images that aren't displayed.  AS doesn't handle the display, it just tells the skin where to find the folder.  Then the skin/Kodi do the display.  The things I would check:

1. Are the images all types supported by Kodi
   
2. do they display properly in another tool (like the Windows preview Window or something like that)
   
3. Is the cachedb OK?  For me the only way to deal with that is to delete the Textures13.db in /userdata/Databases and, in more extreme cases delete the userdata/Thumbnails directory too.
   

​​​​​​​Hope that helps some.