Tenacity Down a bug?

I am currently playing in the Galactic War events (not the one with twelve sets of opponents, but the over-arching solo one that lasts a few weeks I think) when I came across both rows of opponents having Tenacity Down, causing them for one reason or another to be immune to being killed. It doesn't matter who I shoot, they don't die. I've lost three bouts so far trying to find a way through but I am stuck. The screenshot is to show what is going on.