Data chipset blocks all data flow - whole point of connecting to the deaddrop is to get data; and yes, I agree all lines when capping voltage show be checked, though would not be surprised it’s not common for off the shelf usb power isolators to only check the power lines as defined by USB standards.
A USB data-line isolator does not block data flow. Its entire purpose is to alow data to be communicated across a galvanically-isolated gap. It uses magnetic (transformer) or optical isolators to do that.
It blocks POWER flow, while passing data. Look up the ADUM3160 datasheet.
