Well, it is best to directly connect a device like a phone to a PC for best results. Connecting through a USB hub, which must be what your external hard drive has built-in, doesn't always work.
That isn't restricted to MC either. I have had that issue just with Windows and other applications. Usually, if Windows doesn't detect the device (iPhone in this case), the software application isn't going to see it either. But sometimes even when Windows does, an application like MC won't because it is trying to connect using MTP rather than just connect the device as a drive. It may not have helped that you are using a USB to Lightning cable, which means your hard drive is a Lightning device.
Anyway, good you got it fixed, and thanks for the reminder to ask people to connect their devices directly to a USB port on the PC, rather than through a hub.