Fire Emblem Heroes – improper use warning

Fire Emblem Heroes latest update includes a notification warning players against using the game improperly. It does not go into specifics as to what it is warning against.
The full in-game statement reads:

Thank you for playing Fire Emblem Heroes.
Since the release of the game, we’ve detected improper use from some players. Countermeasures are being employed to address this, including temporarily limiting access to certain features.
Players who are subject tot these countermeasures will receive a notification in the “To you” section of the game’s notifications.
We asks all our players to abide by the User Agreement, including the Code of Conduct, as they continue to enjoy Fire Emblem Heroes.