Error when accessing to Cloudflare: 0: Failed to sign certificate

We’ve got an unknown error when SSH-ing to one of our servers through Zero Trust Access. The error goes:
0: Failed to sign certificate

The whole log looks something like this:

OurMacBook-Pro:~ we$ ssh
A browser window should have opened at the following URL:

If the browser failed to open, please visit the URL above directly in your browser.

0: Failed to sign certificate

The error doesn’t occur all the time, but we get that occasionally.

Does anyone know what the error means and how to solve the issue?

I just ran into this. I deleted and regenerated the certificate for the app and all was good.