Just to add for Plex support seeing this, clearly it’s an issue alot are seeing:
https://www.reddit.com/r/PleX/comments/rydmco/something_went_wrong_make_sure_the_server_is/
https://www.reddit.com/r/PleX/comments/n7yx05/plex_import_itunes_playlist/
Has anyone tried and had luck getting this to run?