Not much detail here. A more thorough postmortem would give me more confidence they can recover from another similar issue. Hoping to see one soon.
There's no point in reading these because there's no technical information. Stuff like this is something you sent to your customer because they want root cause.
I know it doesn't tell you much about exactly what happened, but the truth is they may still be sorting that out and focusing on ensuring it does not happen again. An in-depth post-mortem accompanied by a description of the fix would be great. In the meantime, admitting culpability and apologizing are the ideal essential first steps.