Hi, Juan,
Following up on this, I've now updated to Moodle 3.3.1 and (assuming no further problems with user migration) I'm now using the core Oauth 2 authentication functionality.
Is the local_mobile plugin ("Moodle Mobile additional features") still required? Or does it provide additional functionality that is not in core 3.3.1? I notice that "Plugins / ►Local plugins / ►Moodle Mobile additional features" no longer lets me choose the type of login - it only has "Check plugin configuration".
Should I uninstall the additional features plugin now I'm on 3.3.1?
Best,