http://www.alcor.org/cases.html A loooot of them include things going wrong, pretty clear signs that this is a novice operation with minimal experience, and so forth. Also notice that they don't even HAVE case reports for half the patients admitted prior to ~2008.

It's worth noting that pretty much all of these have a delay of at LEAST a day. There's one example where they "cryopreserved" someone who had been buried for over a year, against the wishes of the family, because "that is what the member requested." (It even includes notes that they don't expect it to work, but the family is still $50K poorer!)

I'm not saying they're horrible, but they really come off as enthusiastic amateurs, NOT professionals. Cryonics might work, but the modern approach is ... shoddy at best, and really doesn't strike me as matching the optimistic assumptions of people who advocate for it.