ERR_SSL_VERSION_OR_CIPHER_MISMATCH - no certificate in browsers on a LAN

Hi,

We have a customer that has a Sophos XGS126 running SFOS 20.0.0 GA-Build222. and they also have Sophos Endpoint on clients and servers (all Windows).

They have an external website that they can't reach and where they get this error in the (any) browser:

ERR_SSL_VERSION_OR_CIPHER_MISMATCH

When I check the browser, there is no SSL certificate visible and the connection shows as insecure.

When we access the same website from another location, the website is visible and has a valid SSL certificate on it.
That certificate is issued by Sophos Endpoint EC Root

So I'm guessing that in the location that can't access the website, the certificate is not sent to the clients?

I can't find much info about it except that this should be pushed into the cert store of windows explained in this thread:

firefox error accessing the web with ssl inspection enable - Discussions - Sophos Endpoint - Sophos Community

Can someone point me in the direction I should be looking at ?

Thanks.