I had the 2 instances working fine last year, using the Reddit approach (seperate PC accounts for each instance of Zwift). I upgraded my PC with a much better GPU card and now every time I load the second instance of Zwift and try to go from pairing screen (up to which it works fine) to the ride menu, or just watch, the second instance either hangs, or crashes.
Have the (what feels like) hundreds of updates since I last used Zwift in this way, killed it?