That single dent looks like the sharp ridge between the two extension ramps. If you've filed the ramps that ridge can become sharper and start to dent the case. Magazines that firmly hold the round before it releases don't help. Playing with the magazine lips might work. Filing the ridge flatter might also help but might introduce new problems. Be careful, the risk with filing extension feed ramps is messing with it beyond where it helps.
It is definitely not the deflector - those are flatter dents.
It is definitely not the deflector - those are flatter dents.