As happens on this site, few facts and lots of guesses as to the cause. I think we're missing something because much of the guesses don't make sense for an instructor to do. I hope more comes to light so we can learn from this tragedy. What does concern me is having equipment that is defective, coming up with a work-around that, with little facts, seems flawed and still going ahead. As instructors, we need to know when to say, "Not our day, let's come back". What I have noticed over the past few years and very much over the past year is a lack of time to really teach. We have less time given to us in the pool due to Covid protocols and must work through skills in less time with less time to just play with buoyancy and other things. At our quarry, visibility has deteriorated to 5-7 feet and I am more and more nervous about the safety of my students. Some shops now simply go down to the platform, do the skills, swim around the platform as the "tour" come up, brief the next dive while on the surface in the water, descend then repeat. After that, they leave for the day. We seem to be in an ever shrinking time frame for teaching while trying to churn out very competent divers. This may be particular to cold weather environments. Trying not to judge, but I'd retire from teaching before doing that.
It is so saddening to continue to read stories of student fatalities during training dives. Some may be unavoidable (medical) and some may be all stars completely align for tragedy. However, I grow more concerned about my own teaching in light of the pressures placed upon "finishing" as opposed to letting the student spend tons of time actually diving around during the training dives...and the pool. If it gets to the point that I'm just not comfortable and not enjoying myself (certainly the students would not be either), guess it's time to move on.
Sorry, just my two cents, mostly in an attempt to ease my own concerns.
Rob