Moodle for mobile

In Moodle 3.5.3+, two weeks ago I enabled support for the mobile app and selected one of the mobile app authentication browser options.  I downloaded the app from the Play Store and was able to use our OAuth2 provider button below the username/password box to sign in to our site via SSO.  (Unfortunately, no screen shots.)  Now a week later, I tried to sign in another user by adding the same site to bring up the login view.  Our provider button will not appear and I confirmed that the provider's "Show on login page" option is enabled.  I have tried uninstalling and reinstalling the app and I have tried all 3 mobile authentication options with a cache purge and Android reboot in between each attempt.  This is the official Android app with no CSS customizations.  I checked the output of the REST web service tool_mobile_get_public_config and the provider does show in the identityproviders section.  Our SSO is working as it's the only way to log in to our Moodle site (alternateloginurl is set to use it).  Any advice on what else to check?