I doubt that it is a "growing trend" any more than that bodycams themselves are a growing trend. A certain "loss rate" is seen even with vehicle cameras when it is to the officer's favor.
Personally, I'd make a simple change. The footage has been "lost"? No footage available?
Then either the police are charged with destruction of evidence OR the case goes to court assuming that the lost footage contained the worst possible case.
This case isn't actually ideal, I think, given that the officers apparently signed as themselves. As such, it wasn't the victim who refused medical treatment, it was the officers. Ergo, they're responsible for him. No matter what else happened. They signed the refusal of treatment, they're responsible for his death. Easy.
If there were allegations of forgery, then we might have something more.