Can't access any .netlify.app sites due to a HSTS error and an expired cert

Hello, I looked around and it seems like everyone has issues with SSL on custom domains - but I keep having them with default, Netlify-issued ones!

Wherever they are, keep getting an NET::ERR_CERT_AUTHORITY_INVALID error and any browser complains a HSTS failure because of an expired certificate. I can’t even skip and proceed at my own risk - the sites are inaccessible at all.

Our agency website, clevver-eleventy.netlify.app worked fine on the Netlify domain until some point after we switched to a custom domain, clevver.design which works fine. I’m not sure when it happened and why, but I noticed it after I tried checking out a branch preview, like this one.

The weird thing is that I’m experiencing the same issues on projects I deploy on a completely different, personal account where I just try things out in my spare time. For example this one: https://www.valshuty-ghost-eleventy.netlify.app/.

Is anyone else experiencing these issues?

Hey @valshuty,
Sorry to hear that you’re running into this. I took a look and am able to load your sites, including your branch preview, from Firefox on the US west coast. https://valshuty-ghost-eleventy.netlify.app/ does not seem to exist in our database. Maybe you’ve deleted that site since writing in?

What would be helpful for us in troubleshooting is an x-nf-request-id and some information about your browser and network. Which browser is this happening for you on? This error can also sometimes be caused by interference from firewalls or browser extensions- could either of those be true for you?