It should be a temporary thing. Or not, depending on how Invision has its servers set up.
This 'certificate' is the SSL/TLS credentials attached to the domain name that tell your browser that you are really at the site that you think you are, and are not being spoofed or redirected. I do not know what systems Invision (both our forum software and the company that hosts it) uses to monitor this, but on many LAMP stack (Linux, Apache, MySQL, PHP) these things are automatically corrected in short order by the system issuing a new certificate.
At issue is the time and date recorded on the certificate no longer is in sync with the server system clock.
We will have to wait until it heals, because there is absolutely no one we can complain to. My servers for websites jumped this hurdle with new certs at 2AM or whenever the time rolled. But PN is not on my servers, so... 😄