Please try to run a fresh reinstallation. Here's how to have Zwift do a fresh game download:
1) Open up finder
2) Hold the "Alt/Option" key and click Go > Library
3) Open "Application Support"
4) CTRL-click (or RIGHT-click) on the Zwift folder and move to trash.
5) Re-run download the installer from Zwift.com and run it
That should clear away your old install and download the latest version of Zwift onto your Mac.
From Zwift:
Please try to run a fresh reinstallation. Here's how to have Zwift do a fresh game download:
1) Open up finder
2) Hold the "Alt/Option" key and click Go > Library
3) Open "Application Support"
4) CTRL-click (or RIGHT-click) on the Zwift folder and move to trash.
5) Re-run download the installer from Zwift.com and run it
That should clear away your old install and download the latest version of Zwift onto your Mac.