Some itch.io sites (bitingthebullet.itch.io, possibly others) are triggering an invalid certificate error in Safari.  The site is currently using a wildcard cert from Fortinet.  Your main itch.io site is using a different wildcard from a different CA, so I'm assuming that this is fallout from the Fortinet compromise a couple of months ago, and that somehow the certs on certain sites just didn't get replaced correctly.  Either that or someone is actively trying to MiTM me, but the former seems more likely.