Thanks for following up. When I view on safari iPhone it pops up saying it requires a client certificate then shows two long number/char strings that look the same.
Chrome on Mac just loads the background color of the site and seems to stall. Similar on Windows.
I do have an IIS rule redirecting http to https not sure if that would be causing any issues.
It’s true that the site is sending a TLS 1.2 CertificateRequest message to the client, which I guess is prompting Safari to actively try to authenticate with a client certificate. Maybe you need to configure the web server not to request client authentication.
I developed it with React. Likely more of a React issue and not LetsEncrypt at this point. I did start with create React app, so not sure why this would be.