Dubwool V only taking 30 damage instead of reducing by 30 damage?

Jami3

I had a Snorlax with Body Slam 100 damage, against DubwoolV. It's ability says "this pokémon takes 30 less damage from attacks"....but my snorlax only did 30 damage instead of 70! There were no items on either pokémon. Is there some reason this didn't work? Is this a glitch?

PS there's no tags it will let me put on my message.

Edurandomnumber

What energies did your snorlax had? if it had 2 double turbo energy, then it would do 100 - 30 from dubwool V's ability -40 from the double turbo energies.

Jami3

I don't remember, I'm sorry... But that makes sense. I'll write down the energies if I see it happen again.