Any idea when a solution to the errors when signing up over HTTPS is coming?
A possible solution that I'm positive would work is also enabling Let's Encrypt SSL for the order subdomain, like with the VistaPanel, so there's no "Not fully secure" errors and no "Mixed content" errors, etc.
This would mean that Chrome would still show "Secure" in the address bar, and Firefox wouldn't show a warning sign over the lock, so this would fix a ton of problems with the signup.