Certificate not trusted on mobile network

Hi there -- I'm having an issue where SSL works fine unless I'm on my mobile network connection. To be clear, it's not a mobile browser issue, as everything works fine if I'm connected to wifi on mobile. Any help is appreciated. SSL Labs reports look really good. report1 and report2

My domain is: www.tophermckee.com

I ran this command: certbot --preferred-chain 'ISRG Root X1' as found in this thread

It produced this output:

Deploying certificate
Successfully deployed certificate for tophermckee.com to /etc/nginx/sites-enabled/tophermckee.com
Successfully deployed certificate for www.tophermckee.com to /etc/nginx/sites-enabled/tophermckee.com
Your existing certificate has been successfully renewed, and the new certificate has been installed.

My web server is (include version): nginx

The operating system my web server runs on is (include version): ubuntu

My hosting provider, if applicable, is: n/a linode/akamai?

I can login to a root shell on my machine (yes or no, or I don't know): yes

I'm using a control panel to manage my site (no, or provide the name and version of the control panel): I'm using command line to manage everything

The version of my client is (e.g. output of certbot --version or certbot-auto --version if you're using Certbot): certbot 4.0.0

From the SSLlabs report:

1 170.187.136.30
tophermckee.com
Ready Wed, 23 Apr 2025 04:01:13 UTC
Duration: 60.815 sec A
2 2600:3c02:0:0:f03c:92ff:fea4:610a
Unable to connect to the server

The report says it can’t connect over IPv6.

That’s probably your problem: mobile networks are often IPv6 these days, but your internet provider for your wifi might not be, or it’s broken/disabled somehow.

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