Bugged Gun
99% sure this wasnt confirmed to be fixed, simply putting it here in case devs aren't aware of this problem in the hopes that they fix this in the legendary edition. A few months ago I ran into a bug for the first time in ME3 where a gun couldnt kill dr eva before she reached you at the end of the mars mission. When i remembered this I quickly uploaded it to youtube so i can link it, far easier to understand when you can see it in front of you.
Mass Effect 3 Mars Bug/Unintended Mechanic
Pretty sure it is called the acolyte. I had never experienced it before because i'm pretty sure it is a dlc gun and I just never had it on my original playthroughs without dlc.
The gun clearly knocks her back but it seems this 'cutscene' is timed so after a specific time the cutscene of Eva whooping your butt will play even if she isnt close to you at the time.
This gun does not appear to be able to kill her, I attempted it quite a few times and even with my timing on point I only managed 2 shots and couldnt stop her with them.
The gun charges up which makes it super tricky to use in this specific scene because the time slowdown really messes with your muscle memory and visual queues for when the gun is ready to shoot.
If this gun is going to be available in MELE because everyone gets dlc I hope they either change the scene so knocking her back buys you time, so the gun can take her down OR just deny access to the acolyte on Mars and unlock it after this mission.
This is mainly an issue because if you want to change your gun you basically have to restart the Mars mission and consciously avoid this gun.