After password reset and logging out every where, my family cannot change to their specific user in the Plex Amp app. All apps and devices are fully updated. Uninstalled app and restarted devices, reinstalled app, After signing in and selecting a library, tap on settings, account, switch user and selecting a user; the app signs out.
In that case you might want to verify which version of PMS you’re running.
If you’re on a version between 1.41.7 and 1.42.0, you should update to the latest public release.