If a user has not modified their settings, then they default to the account settings. If settings on the account are updated, this causes the user’s settings to be updated. However, the
user.settings_updated webhook is never sent. Per the documentation, this is incorrect behavior:
The User Settings Updated event is triggered every time the settings of one of your app users or account users are updated.
Because Use Manager OAuth apps cannot access account settings or webhooks, it is impossible to keep in sync with the user’s current settings via webhooks due to this bug.