[hoschilo]

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.  

Sorry my post was mileading a bit:

- all images are supported by Kodi and displayed correct if the artists are played individually

What is happening I belive is the following (for my Herbie case):

- AS getting information about multiple artist and sildeshow directory is set to Herbie Hancock artwork Folder on my NAS as the first found artist
- AS continues in getting additional art work for the other artists and copying them to the merge folder in my profile
- Before setting the merge folder to the slideshow folder the script stops due to another UTF-8 Problem (sorry for that)

Can you set the sildeshow directory from the very beginning to the merge Folder once you have indentified that there are multiple artists? Even if the script fails due to decoding error the slideshow of the available Images will continue I believe.