I have a new Mac Mini and have just updated to Mojave 10.14.3, and the same thing is happening that happened on 10.14.2 - it crashes. I’ve tried with the Iphone companion app on and off and it makes no difference. I get to the point of pairing successfully, and then it crashes every time before the course/workout selection screen.
The instructions for reporting error logs tells the user to copy/paste the text into a Zwift website with a character limit that makes it impossible to copy/paste even a small bit of the text. If you jump through a few hoops you can upload a file, so I had to .pdf the text and upload that instead of copy/pasting it.