Okay, that seems to match the serial / fingerprint of the intermediate certificate I’ve got so either the root certificate is not being sent with the rest of the chain or it’s corrupted somehow.
Given that people are only experiencing this on certain browsers/systems, what’s weird is that it works fine on my Android 6 phone with Chrome. I’m guessing the site isn’t supplying the root certificate and some devices don’t already have it in their Trusted Certificates store on their device.
Without having a device where I get this error, it’s harder to diagnose further but thank you for the help @danielccm!
@discourse @codinghorror is this something you need to correct or SmartThings staff?