I think the only way HC-05 can involuntarily disconnect is because of inadequate power to Arduino, and the fact that the Mac soldiers on is just coincidence, but at least you have proven that your wiring and code are kosher. If the power is indeed adequate, all your problems are at the PC end, about which you say nothing. The standard terminal programmes, RealTerm, Putty, etc., should be fine under Windows 10, which has been around for quite a while now. You might try proving the point by talking to a phone instead, again using a standard terminal.