HTTPS connection reset - Firefox & Chrome

Hello

I have a problem with one web-application since I switched to XG18.

I have running EcoDMS on a linux server (10.100.10.x) with HTTPS enabled for the Web-Interface (I tired self-signed and wildcard certificate). When I try to connect with my client (same network, local, 10.100.10.x) with Chrome, Safari or Firefox I've always an HTTPS Error (ERR_CONNECTION_REFUSED e.g).

With Internet Explorer I don't have any problems.

I have no DPI or WebProxy enable in my local Network as far as I can see (I'm no Sophos XG expert).

Whats the best way to analyse this on my Sophos XG? Or does someone already know this issue?

Cheers,
Patrick