I'd need to dig through our code to be sure of all the details; however, this is what's mostly likely going on: Now this is where things go wrong. On macOS 15, our app seems to be gracefully terminating (we attached it with lldb, and it shows that our app returns with 0 when we click Continue“), which is fine. This is likely the classic macOS app lifecycle, which involves your app receiving an AppleEvent and then choosing to exit. Strictly speaking, your app wasn't terminated— the system asked it to quit, and it eventually chose to exit (it wasn't not required to). However, for macOS 26, though, it seems that TestFlight just directly SIGKILLs our app. This sounds like the sudden app termination lifecycle, as described here. In that approach, your app is responsible for telling the system when it can't be killed, and the system is allowed to terminate your app any other time. The link above has the full details on that. However... (indicated by lldb), which means that all of our app's child processes