I’ve been unable to narrow down a similar bug where starting/stopping Siri triggers the proper interrupt begin/end callback, but subsequent starting/stopping of Siri only triggers the interruption begin callback. I’ve seen it happen in the sample app, but it takes some serious button mashing.
I’m on a time crunch so I ended up moving my interrupt functionality to happen via the applicationWillResignActive and applicationDidBecomeActive lifecycle callbacks. Just wanted to leave this here for those stumbling upon the thread looking for a solution, albeit not necessarily the proper one!