Update: Apple Developer Technical Support has confirmed this is an iOS bug and asked me to file a bug report. It's filed as FB25086794 and linked to my DTS case. The same behavior also reproduces on iPad with iPadOS 26.6, so it isn't limited to iOS 27. If you're seeing the same thing in your app, filing your own Feedback report and mentioning FB25086794 will help Apple gauge how many apps are affected. I'll update this thread if a fix ships.

One small precision point: “responds within 0.05 s” describes requesting playback, rather than audio actually restarting. Our latest logs show the play request immediately after the signal, with playStarted about 0.31 seconds later. The main finding still holds: the long wait comes before the resume signal.