Elite Four loop

I was battling the Elite four, I started off with Kayla and I battled until she sent out her sylveon, I used a shadow ball and it did little so what I did instead was use fly. In turn, this happen.

Zori (Mega Delta Charizard): Flew up high
The Foe Sylveon used Hyper Voice
The foe Sylveon’s Attacked Missed!
It doesn’t affect the foe Sylveon

This kept happening over and over and you can’t stop it. I wondered if it had to do with my move poll so this is what my Mega Delta Charizard had, Dragon Pulse, Shadow Ball, Lunar Cannon, and Fly. So if anyone knows why this happens please help!