Nick_Pyner:
Yes. Probably has nothing to do with communications, and quite a lot to do with power supply. Where is the 5v connected to on Arduino?
5V Powerbank/battery USB cable into the micro USB plug on the arduino micro.
5V on Arduino connected to VCC on HC-05.
The same problem occurs using a 9V battery through a power supply module or a phone charger from the mains into arduino micro usb plug.