There have been several cases of BPI pressures being off on shotgunworld.com and duckhuntingchat.com
I don't remember all of the reloaders that have had loads tested but derbyacresbob is one that had multiple loads sent out for testing that came back over pressure. There are others that would put their hands up if someone cared to ask. They aren't all Longshot loads either.
Longshot has a high nitroglycerine content. It works well for a lot of applications but when it goes over pressure, it goes quickly.