after starting a mono steel type run i need to cry. A lot of good steel types not implemented yet (Scizor, Skarmory, Klefki, Metagross, Honedge, Escavalier, ferroseed(why are you mocking me behind those bars!!!), the list goes on...)
Did you fight perhaps on the crystal cavern field? You should check the field effects if so, because rock attacks can get random additional typing while fighting on those fields
Decidueyes Hidden Ability "Long Reach" seems to be bugged, occasionally decidueye or its opponent miss 100% accuracy moves like leaf blade or sucker punch.
Fights were on forest field and decidueye was holding a miracle seed, if that helps anything...
Since i changed its ability to overgrow 100% accuracy moves never missed