Placing a stop didn't hold priority
Steps to reproduce:
1. Have The One Ring in play with a number of counters on it equal or greater than your current life total
2. Place a stop on the Upkeep/Draw step of your turn
What ends up happening is the trigger from The One Ring gets placed on the stack and immediately the game passes priority to your opponent and you lose, even though activating The One Ring or casting instants in your hand are valid actions that can be taken.
What I would expect to happen is that since you have a stop placed on the phase, you would be given priority after anything is placed on the stack similar to full control. This cost me a game in which I had instants in my hand which would have allowed me to gain enough life to survive the trigger.
It's hard to see in the screenshot, but it was my turn during the upkeep where the stop is placed when I lost.
A current workaround would be to slow the game down to an annoying crawl by playing the entire game in full control to prevent this and other buggy automation present in the game. An appropriate fix would be to just have a stop force full control at the start of the stopped phase and last until cancelled or the phase ends.