I've never encountered this issue. Flame Vipers have definitely shot devices in my campaigns in the past, but that's a very rare scenario to speak to definitively given the number of enemy units in the game.

So, let's do some basic troubleshooting...

After you uninstalled all other mods for a clean environment, did you validate the XCom files and delete the base game config folder?

https://support.2k.com/hc/en-us/articles/217132417-XCOM-2-Basic-Tech-Troubleshooting

Are you staging the mission using the SDK's Debug feature or dropping a Flame Viper into an actual game mission using the command console? In either case, I assume the Flame Viper is not under Red Alert behavior when the event occurs, otherwise she would have used Seething.

When you mention a soft lock, are some or all of the following true:

-The unit pawns are still playing their idle animations.
-There is still environmental sound present (music, birds, etc.)
-The camera focus is a Flame Viper and the game appears to be waiting for her to take an action.

If the above statements are TRUE, try this as a test:

Open the Flame Viper's config file XComAshFlameViper.ini and make the following edit:

---CHANGE---

ASHFLAMEVIPER_SEETHING_ACTIONPOINTCOST = 0

---TO---

ASHFLAMEVIPER_SEETHING_ACTIONPOINTCOST = 1

Be sure to DELETE your base game config folder after the edit and then stage the event.

Meanwhile, I'll set aside some time to stage something in my own environment. To be fully transparent, if the edit to the config file doesn't change anything, then it's unlikely an issue with the Flame Viper. The 0 Action Point Cost is the only remote, outside chance that the issue could trace back to the Seething Ability.

I've been unable to recreate this issue since the first two times, so im willing to assume it was possibly unrelated.

Also, all of the following was true.

Hey Cpt.Haxray,

With all of those above conditions being true (especially the camera focus part which was kind of a smoking gun I was looking for), I think I'll go ahead and tweak the Seething Ability code slightly anyway. There's a better way to define 0 Action Point Abilities now that I used with the Muton Destroyer that only requires 1 more line of code! Without that one line of code, I noticed the game waiting for the alien to use its 0 Action Point Ability in Mind Control scenarios. So, I thought maybe, kinda, sort of, on an outside chance this was a similar edge case.

I think the Flame Viper deserves a v2.0 at some point anyway! It has been years!

Thanks for the update!

Also had a softlock with Mod Jam.
A mission to destroy an enemy device. The viper was fightning 2 zombies that stood around it. It attacked with some AoE flame attack thing, and it just never stopped the animation. Camera endlessly zoomed in on the Viper with the flames around it.