WAN disabled, no WebGUI on OPT1

[sgw]

pfsense-2.3.4p1 on a Netgate SG-4860:

until last friday we had 2 DSL-lines going to WAN and OPT1, now the DSL to WAN has been removed (and will stay away) and the 2nd line is now the default. I disabled WAN interface, changed the gateway for OPT1 to the default gw and edited stuff like which interface the VPN tunnels run on.

Edited the DNS entry pointing to the FQDN for the firewall to the new IP.

Things work, IPSEC tunnels up, portforwardings work.

But I can't access the webGUI via FQDN from remote. There was and is a firewall rule allowing my static IP (of my office here) into the firewall. I can ssh, but https fails.I played with the fw-rules (allow all ports, allow port 443, etc), rebooted the firewall etc

It seems that I get through the fw. nmap shows open ports, "telnet 443" shows "Connected to" ! But no GUI in browsers.

We maybe reconfigure the firewall to run the now only DSL line on physical WAN instead of OPT1, but I assume that there is noc functional difference, right?

pls advise, thanks, Stefan

PS: I use acme-package to use LetsEncrypt-Cert for the https there. The FQDN is correct.