I have been running Zwift on a Windows 10 laptop without issue for the last 5 months. After the last update on Tuesday, Zwift has been hanging on the pairing screen. It just sits in a loop, the buttons cant be clicked and only one in ten attempts to get to the next screen. Once in a ride everything works fine.
Essentially after hours or uninstalling and reinstalling software I found the issue to be the ANT+ dongle. As soon as I removed it the pairing screen behaved as normal. This has never been an issue before so I believe the update has introduced a bug of some sort. Hopefully this helps someone as I have been trying to log in from an hour before an event at times just to make sure I am in.