Invincible raider, anyone encountered this before?

I was just on Riven Tides at the hotel trying to do the trials.

At about 17 minutes left in the raid, I heard someone so I called out "hello friendly".

I hear someone on the prox say "unfriendly, I'm here for the PVP", and it sounded like it was above me.

I take a zip to the top and climb on the roof, there's a raider there and he's faced the other direction.

I unload my Vulcano IV (10 shots) and hit 9-10 of them and the raider doesn't go down, I don't even recall their shield cracking. He says "dumbass" and starts shooting an anvil at me.

I run and head straight to the hatch.

The after raid summary shows that I did no damage to him.

Anyone seen this before?