could it be as simple as you didn't format the USB to fat first? you alluded to a Mac Usb..your question is "why does the live usb not work?", right?
if we are talking about a usb that wont boot the iso, then what alternatives were in that solus link for mac? only etcher? I wonder? since live iso takes about 5 minutes, I'd say keep trying changing it up every time. DD method works for me. Does DD work in Mac?