I have been facing this peculiar issue from past several months. Whenever I select a file and choose Move to Trash from the context menu OR highlight the file and then press Del button, the file takes forever to delete. The rotating circle immediately appears in the taskbar but file isn't really deleted and the operation keeps going forever.

BUT if instead of Del, I press Shift+Del to permanently delete the file, the operation executes normally.

I am not sure what is the root cause of this behavior. The command rm foo.bar works fine from the terminal, so I am assuming it has something to do with Dolphin