Thanks for reaching out to us about this - we'll be glad to help you out here.
First thing you can try here is running a clean reinstall of Spotify on your PC. This will make sure you get the latest app version with all necessary updates.
If the artist still doesn't show up in the library after the clean reinstall you might need to check the hosts file for entries that need to be removed. Follow the steps described here on how to do that.
Keep us posted! We'll be happy to lend a hand if you need more help.