After 8 locked games, I can confirm that the card causing the locks is Vraska’s vanguard.
I am not sure why it’s causing the game to crash. I took it out of my deck and the problem went away.
You can watch the lock happen here: https://photos.app.goo.gl/w96D7oUFGEACAwkbA
The combo I was going for was to have Ajani’s vanguard and Vraska’s vanguard in play to create the assassin tokens that block stuff. Seems simple enough.
I play tested with many different creatures with deathtouch to get the same effect.
As long as I had Vraka’s vanguard in play, the game would eventually lock up.