Frost Core at Molten Vault; Cannot retrieve from boss fight area

As you can see from this screenshot, once you're done fighting boss, you can't go back back to platform level with that quest item Frost Core. I remembered before 0.5, there's a check point appearing after killing the boss. Maybe in Endgame maps it works but not campaign? I'm not sure.

So, what happened in this picture, I TP-ed back to base, then use Waypoint to run back to the spot at the top again. Of course, with the boss dead, there won't be a way to go down there with the "Arena" label.

+1 for this problem!

For me as I went through the map the first time, I could hear the frost cores drop, but even with the loot filter off (None) there was nothing to pick up. As I walked over where it was it made the drop sound again, so it was there but filtered.

Further on when I got to the frost core socket structures, I had none to use.

Then when I got to the end and downed the boss, I teleported out and came back. At that point two frost cores dropped at my feet and I picked them up, but since I was still in the boss trench I had no way to get back up out of the trench.

So I teleported out again and came back through the waypoint, but then the frost cores were automatically removed from my inventory so I could not complete the parts of the map requiring the frost cores.

Yeah, the only way is to re-run the area again, holding Ctrl and clicking the waypoint for a fresh session. Annoying... This can be easily fixed if they put back the access to go back up from the boss fighting area again. I am not sure if I've seen this in campaign or not, but at least in 0.4 endgame maps, it was present, or have I remembered incorrectly?