Had a mission progression bug where just as the first void cascade was sealed someone joined, (I wasn't host) and the game lagged for a second as the player joined. Which made the next objective timer stall at 30 seconds permanently. Only after a host migration was it fixed and continued as normal.
The lag from the player joining is the only cause I can think of. It's the only time this has happened to me after a few dozen runs of void cascade. I was in a full squad on randoms.