While this is fairly likely, it's not at all unavoidable. I'm usually last in line with my family and always have an unobstructed view. My wife and kid know how to fin without silting things up and have good enough buoyancy control that they don't smash into the sides or overhead.
12 year-old descending at Punta Sur
+ eleventy billion!
It is indeed scary to get stopped and potentially dangerous. My very first time there the woman who zipped in behind my wife and ahead of me stopped dead in the middle. I would have backed out but the guy behind me ended up with his head between my ankles and didn't seem to have the ability to reverse. I'm sure she wasn't stopped for an hour and a half, but it felt like it. I never did figure out why she stopped.
13 year-old exiting Garganta del Diablo