• Engine's motor swapped with ÖBB 2095 014-3
• Received motor from her sister is confirmed to be a bad runner on this engine as well, so issue is the motor itself
• The faulty motor has been fixed: the solution was to reduce the torque applied to the side bolts that holds the carbon brushes of the motor; at least one of them was interfering with the current collector between pole 2 and 3

After the fix the motor is running very smoothly and drained current is within expected values.
The engine still holds sister's motor: it might be swapped back in the future (but they are identical).