I followed advice on building more shell layers, pre-steaming the pressure cooker before putting in the shell, steaming for a short time (30 mins instead of 2 hours) and repairing cracks /adding another shell layer after vitrification. I have one final problem with a frozen surface in parts of the cast. Here's the video of this attempt:

Here's the frozen effect. I poured at 950-970 and I skimmed a film of metal off the top, but it filmed over just as I was pouring.