so last time I played was in 5.1, but since we've gotten 7.1, I tried playing in the latest update but the "outside the law" mission which was impossible to continue before is now completely skipped

all the characters and the map act like I already finished it, but it still appears in my quest log as unfinished, I've yet to fight the invasion that happens in 6.0

any way to trigger the mission? or at least get a 6.0 file so I can try to get it in that version and then pass to the latest version?

Well that's certainly strange. 

Do you have Discord? If so, join here and DM me (Asher). I can send you a 0.6 build, but I'd also like to get a copy of your save if I can. I'd like to reverse engineer a solution to this!