Dolphin has a problem with handling paths pointing to 'Trash'.
When launching the Trash by clicking on the trash can, the dolphin windows is launched with URL: trash:// which is not what it is expecting. Instead, according to dolphin, it is expecting the correct path to be trash:/
You may have (unintentionally) made dolphin the default file manager for opening windows.
Undo that by following the steps below:
Install exo-utils
sudo apt-get install exo-utils
Run it
exo-preferred-applications
In the Utilities tab, under File Manager, select Nautilus back and select close.
After that, try to open trash again, it will open correctly in Nautilus, not in dolphin.
Reference: https://help.ubuntu.com/community/DefaultFileManager