I’ve noticed that Plex shows different error messages if you try to play a removed item which is still in the library trash.
If you try to play it on Plex for iOS it shows this error message
On Plex for tvOS it shows the same text as on iOS.
On Plex for MacOS it just shows a empty XML Window without any information:
Wouldn’t it make more sense to replace this empty XML window with an error message to notify a user that this file is currently unavailable? Because I think this empty media information window is not very informative. 
Or is this a cryptic feature in a bug camouflage? 
