I have the tooltip set up to show which mogs I don't have from enemies (that should drop things I can equip according to wowhead).
This is what it looks like when working (TOOLTIP IN BOTTOM RIGHT CORNER)

and this is what I see when it doesn't work

Settings

Debug mode does not change the behavior.

Imp Mother Laglath does not drop anything specific.
Arclight only has an achievement criteria and the Arclight Jumpers, which are not useful for your class.