Thanks Guys - I tried "mac pause" - it didn't seem to help then I update the firmware to 1.0.0 and that fixed it (It had been 0.9.5).
It did take a few goes to get the update done - the window crashed during the standard update and I had to resort to bootloader mode - the crashing issue with the Lora development utility seems reasonably common.
But I'm up and running on 433 - cheers!