Hello, first of all my apologies if is not a bug, I just want to notice you out about a little mistake in the legality checker.
I had a legit Numel, so using PKHeX I made it shiny and evolved into a Camerupt.
The legality checker says that the "encounter" is not valid. So I checked the location and it was ok.
Seems like the problem was the lvl (it was lvl 16) so I think, it would be less confusing if that advertisement is switched to "Not a valid level" or something else.
Thank you for your awesome tool, and sorry for my crappy English!
Here is a proof: