That's a good news! I upgrade devices to iOS 15.1 beta 2 (19B5052f) and this issue doesn't happen. By the way, my devices are iPhone 8+ and iPhone 7.

[Update the status] I upgrade devices to iOS 15.1 beta 2 (19B5052f) and this issue seem to be fixed. And my devices are iPhone 8+ and iPhone 7.

The official iOS 15.0.1 is released. Unfortunately, it seem to no any patch about fairplay playback.