No database selected error after explicit declaration_base

Question

I'm having this issue, where sqlalchemy does not recognize the database, even though it is declared with declarative_base. After trying to run a simple query of session.query(AppGeofencing).all() I get sqlalchemy.exc.OperationalError: (pymysql.err.OperationalError) (1046, 'No database selected').

The table is declared as

Base = declarative_base()
AppBase = declarative_base(metadata=MetaData(schema='app'))

class AppGeofencing(AppBase):

    __tablename__ = 'geofencing'

    id = Column(INTEGER, primary_key=True, autoincrement=True)
    name = Column(VARCHAR(45))
    polygon = Column(Geometry('POLYGON'))

    def __init__(self, name=None, polygon=None):
        self.name = name
        self.polygon = polygon

The case is only with this table, because I have also done similarly for other tables, and they work just fine.

After enabling the logging for sqlalchemy I can see that is does indeed create the correct query

INFO:sqlalchemy.engine.Engine:SELECT app.geofencing.id AS app_geofencing_id, app.geofencing.name AS app_geofencing_name, ST_AsEWKB(app.geofencing.polygon) AS app_geofencing_polygon 
FROM app.geofencing

but somehow it cannot determine the database to use? Does anyone have any idea, what could cause such issue?