Thanks for the info - I was afraid that this was the case..
I did try a hub attached to the OTG micro-USB port, but it only recognised both the Ethernet and Bluetooth adapters at the "full" (slow) speed setting..
At the "high" setting, I get:
usb 1-1.4: new full-speed USB device number 76 using dwc2
usb 1-1.4: device not accepting address 76, error -71
usb 1-1-port4: unable to enumerate USB device
- and lsusb only shows the Ethernet adapter, and hub/s..