Yes, there are problems with the Etron USB 3.0 host controller.
Currently all external HDD enclosures with JMicron JMS539 chipset will likely have similar problems in conjunction with Etron. The HDD is disconnected during file copy operation.
Could you please specify the exact type of your external HDD enclosure?
You would have no problems if the USB 3.0 host controller was the well proven NEC chip. Unfortunately Asrock has chosen the Etron chip.