As far as I know, this hasn't been addressed anywhere else. It's an obscure problem that I've never had to deal with before.
No other games but Pt have this issue (as far as I'm aware). I enjoy battling my friend locally with teams full of shinies. Mix and standard battles work fine. Yesterday, we decided to do a Double battle so I could test my Cherrim in a more-friendly environment. My opponent sent out two shinies, and it came up with one of those blue error screens. Next thing I knew, I was looking at the lady two down from Teala. We retried several times, switching up our teams and order, but we got nada. Every attempt, after the shiny sparkles from my opponents' pokemon went, it cut off. Mine never came out regardless what side of the room I was on. What's wrong here?