Many times when right-clicking another player to inspect, the window with their gear/stats/bio does not appear. It will sometimes work by showing the empty inspect window manually then try to inspect again. I have never found a rhyme or reason for why it succeeds or fails. This is using the default UI.
Create a macro that says /inspect_player %T and when right-clicking fails, target the player and hit the macro. It's not a fix but it works
Confirmed -- great tip! I also found that if you type the command with the player's name instead of %T, you can inspect them from anywhere in the zone, even if you can't see them.