During the last phase, I got killed, reloaded the autosave but the game threw an error that files are missing. It's those weird errors from Aegis/Atlas (hope I'm not the only one having them). But except this time they broke the game and I can't load up.

So somewhere around where you're defending right? I'll take a look

Just did a number of playtest, even some with compatibiility data, and i haven't encountered the issue mentioned. Please make sure you have all required items and turn on the referred DLC. :)

Oh..yeah. My bad. I didn't enable the DLC/compat. mod....well, live and learn LOL. I guess there would be a way to enable it and force users to have it before the mission can be started, might avoid further dumb questions from others haha.