Pure Heart Bug?

i use Roxie and choose weezing with Blow-away bomb ability for 10 damage on keldeo-GX
and i have mimikyu on bench and when i use zoroark-GX to attack it say
Pure Heart prevents damage

and next turn after this i use gastly evole to gengar with shadow pain ability it cant damage on keldeo-GX too

This issue doesn’t exist anymore