I have been involved in a number of failure investigations.
The most recent and detailed of which is the hard start of the Firebolt 150B at the end of the first year of project sparrow. The Firebolt 150B is a 15 kN regeneratively cooled, LOx, Ethanol rocket motor. I was responsible for safe-ing the system after the anomaly. The team and I cataloged over 130 different objects. The data we collected was invaluable in eliminating possibilities from the following root cause analysis and provided the foundation for getting the Firebolt later successful hot fires.
I was acting as a photographer for another team when their rocket failed on ascent. I quickly stepped in to help with the post-flight review, and we found that the fins fluttered as the rocket went transonic. The flutter became so strong that the fins hit each other before breaking off. In the pictures below you can see the imprint of another fin and the undamped oscillations in the exhaust.