[US/UM] That's super effective?

[Saltysparrow]

So bit of a strange story on this one it happend some two weeks back. I was replaying through my sun version getting ready for the ultras to come out. My team was comprised of a full roster of wonder trades and I got one of my favorites dritini so he was my buddies through the whole game. It happend in the latext game he evolved into dragonite and I was fighting an ahlolan muk my nature was modest and my moves were Draco meteor, thunderblot,icebeam, and hyper beam. Thats when it happend my game told me that hyper beam was super effect aginst the poison dark type. I though  that was super weird. It happens one more time ( different Pokémon different move should have been just effective) during my playthough of ultra moon. So here is my question what could have caused this could it be related to my Pokémon affection toward me the trainer and also have you guys had something simular happen to you?

[stephenWITNESS]

That's really strange. I've never heard anything like that happen before. Did you end up using hyper beam on the muk and was it super effective?