This only happened once but for some reason, when my Luxray beat a Wingull in the Stormy Sea/Whirl Islands, she didn’t get any experience. However, the following Tentacruel and Wingull did give her experience. Why did that one Wingull not give Luxray any experience that one time?
Put it on the bug tracker.
It depends. For example: the Pokemon Tournament. You didn’t get any experience from it. It depends on when and where you battled the pokemon. That’s my only theory.
It probably is a bug, as VortexInfurnus said, put it in bug tracker
I’ve discovered it’s actually a glitch with my Luxray in general. There have been a few other occasions where it hasn’t received any experience points after winning a battle. It’s not preventing me from levelling it up but it can be a bit annoying.