Hm? I have not come across such issue in a while
but yes I would recommend creating save and placing down anything from your library you want to keep in there (save it obviously) and then going My files -> The Sims 4 -> Tray and deleting everything in that tray folder (not the directory)
as it sounds like your tray is broken
you can then re enter the game and put things back in library from the save you created
also there is no partially deleting your tray you either delete all of it or none and combining trays will result to broken tray
if you want to delete specific thing in your library that has to be done inside game but if your tray is broken already it does not work
