Bungie, Twice tonight did the Legend Seraph bug out and not allow us to continue. Right before the open room with Briggs. Also, no crouch/rift function, which is really handy. Nothing like wasting 2 hours for nothing, on an already endless grind of a game. You own it - fix it.
Quickest fix for no crouch is just swap out your class ability and set it back, a little easier than messing with keybinds. For the progression, I've found making sure all enemies are dead before shooting progression panels seems to prevent the issue so far.