After migrating to a new Android phone, a few specific apps stopped launching. Amazon Shopping and Kindle would freeze on a blank white or black screen for a while, then close on their own. Reinstalling, clearing storage, updating the OS — none of it helped. Going through the usual support steps changed nothing. What finally fixed it was clearing the storage of every Amazon app at once. Tracing the cause through ADB logs, it turned out that authentication data shared across multiple apps had become inconsistent, and the auth-retrieval step at startup was deadlocking. The incident itself happened with a specific Pixel-and-Amazon combination, but structurally it's a pattern that can hit any app where "authentication data shared across apps" meets "many subsystems initialized in parallel at startup for speed." It's worth knowing about whether you design SDKs, build apps, or handle ops and support, so I'm leaving it here as a case study. Note: This happened on my own device, with my own account.…