@EA_Gunner
Another finding:
This time our guy that soloed it the last time had trouble getting through the first phase. So we've decided to test new apporach.
Few of us attacked but we organised it in a way that only one player was attacking at time. One by one we managed to almost take down the first phase (around 80% done). Then, guy with SLKR soloed the rest, max crate reached no problem.
So, as I see it, our findings leaves only two things can cause the bug:
1) Multiple players attacking at the same time
2) Some problem with transitions between phases when multiple players are participating
To other players reading this:
Try to solo it if you have the option. If not, try to organise it in a way that only one player is attacking at time then share your findings here if you can, I think all of us will appreciate it.