Crashing on login

Running Zwift sandboxed under Win 10.
Got updates yesterday on the unsandboxed version, so I wiped the sandboxed version and recreated it to pick up the updates.
Tested both versions at that time and everything worked fine.
A few hours later (18:00 or so EST), the sandboxed version hangs immediately after the “Login successful” message appears.
I have attempted various combinations of deletes, restarts, reloads and system updates and cannot get the sandboxed version to work, even if the unsandboxed version is not running.
The unsandboxed version continues to work fine and I can log in with my account on that version without trouble. (Usually, that’s my wife’s version…)

Any ideas?
The sandbox is exactly as set up in the Random Neural Misfires description of running multiple instances of Zwift found here: http://blog.gnu-designs.com/howto-run-multiple-zwift-sessions-on-the-same-pc-windows-only/

Thanks!