The hole that connects the two sides of the leak down tester is pretty small....... so it doesn’t take much of a leak to not be able to build pressure.
If the leak is bigger than that orifice in the gauge...... you’ll get nada.

That being said, the only way I can see it being a ring issue is if the comp rings are either broken, or........stuck/seized into the ring grooves.

Be interesting to see what you find.

Did you happen to do a compression test on that cyl as well?