Laravel application SSL issue on some 4G networks

Hi,

I have a Laravel application deployed on an Ubuntu server with nginx and Certbot for basic SSL.

It was working fine until recently when I moved the application under a subdomain. I created the new certificates and all seemed to be fine.

But we got a few customers, complaining they cannot access the app as they are getting SSL ERROR when accessing the application on their mobile devices on the mobile network. Although, they reported they can access it via the WIFI network on the same devices.

I run some investigation:

1. Specialised SSL checkers show that the SSL certificate is set correctly and it's all fine.
2. The users who cannot access the app are all from the same mobile network (operator) in the UK.
3. It doesn't work on both platforms Apple (iOS) and Android via the 4G/5G networks but works fine on the WIFI Networks.
4. When they access the app nginx logs an error: 2024/06/24 13:07:50 [crit] 1396868#1396868: *1822 SSL_do_handshake() failed (SSL: error:141CF06C:SSL routines:tls_parse_ctos_key_share:bad key share) while SSL handshaking, client...
5. I asked two friends of mine who are on the same network as the customers who highlighted the issue. One has an iPhone 12 and for him, it didn't work. While the other one uses an iPhone 15 and it worked for him.
6. I also ran the apt update and openssl update on my Ubuntu server and restarted the Nginx server but nothing changed.

What could be the issue? And most importantly what could be the solution?