Trying to find out the facts. Historically the Proof Houses have always been very diplomatic and guarded with making public statements, and perhaps rightly so. If we need to know, they invariably publish a pamphlet or issue a statement.
As far as I can ascertain there have been a relatively small number of incidences to date.
When you consider the number of guns proofed and re-proofed per annum the failures are indeed very small in numbers. It is very early days as yet but it is my belief that it may well be a problem associated with barrel boring, choke profile or metallurgy. Safe to say that it is my belief that any reasonably sound gun with a minimum (less than modified)of choke constriction should (will?) pass proofing.