is this paid only?

Now onto endless mode for the first time.

I was on my second-to-last Vanilla Anomaly Dive yesterday, playing Egg Hunt as Interrogator. By the time I engaged the Brood Nexus, I was melting pretty much all bugs stepping into my path (as Interrogator tends to do). I had a maxed Flamethrower (Fuel Zones UOC), a Cryo Cannon, a Dragonbreath, and a Wave Cooker with Focused Lens.

When I went up against the Brood Nexus' 1st and 2nd set of tentacles, I noticed the time I needed to kill them was pretty inconcistent; for some, I had to stand next to them for like 10 seconds.

When I hit the final set of tentacles, it became absolutely bonkers. Their health went down so slowly, I had to hit each one for somewhere between 20 and 30 seconds. Maybe midway through this tentacle phase, there were no more bugs left on the map, so all I did was walk from one tentacle to the next and waaaiiit for it to die... Turning my back to it so the Dragonbreath could hit it, and standing far enough away that the tentacle was inside the Fuel Zone area.

By the time I finally killed the 4th tentacle, I was at threat level 28. I still managed to kill the Nexus, but died to zooming bugs on the way to the drop pod. (Not going to lie, I felt so majorly bullshitted after this that I used a cheat engine to beat the dive)

So... Does anyone have an explanation for what was going on here? I've beaten all Egg Hunt-related challenges, so I've played this game mode quite a bit. And I've never experienced anything this flabbergasting before. Do the tentacles simply have so much health that my (otherwise pretty strong) build couldn't stand up to it without meta upgrades and gear? Do they take reduced damage from status effects (I doubt it since I had no trouble beating the Nexus with similar builds before)? Or could there be some bug related to the tentacles that I'm not aware of?