I reported this last night to Kabam (case #04876147) but they didn't respond and silently closed the case without comment.
Not gonna let that die quietly!

I was in a dungeon run last night, just started and defeated Archangel on node 1. Then the game sort of blipped, went back to the map screen and Archangel was still on the node, full health.
And I couldn't re-enter the node to fight him.
I quit the game entirely, closed it, and reloaded the game. And then I couldn't even enter the dungeon. It'd just jump me back to the home screen every time.
Which left my partner in the lurch, no way he'd be able to complete it on his own. Wasted my time of course, not to mention meaning there's no point in even trying to play the Dungeons because how many times would that happen again? It was only my third round. Looks like others are also experiencing the same issue. Kabam seriously needs to stop hiring bro-grammers.
Here's a video showing me trying to re-enter the node:
https://www.youtube.com/watch?v=dxjvN7ngPDs