SSL Expiry Sensor stopped working

I have a curious problem, which I have been trying to solve for the last week. Despite trying various options I seem to be making no progress. Therefore I am hoping someone on the forum can point me in the right direction.

My Setup:

QNAP NAS running Home Assistant 0.99.3 in Docker. I also have two RPi 3+ with Pi-Hole and PiVPN.

I have also setup remote access with SSL and duckdns. That means that I can reach my server both at home and away using my duckdns logon over https. So far, so good.

Last month I received a letter from my internet provider that they needed to replace my router/modem (Fritzbox 7390). I never had a problem with the device, but they said that it would longer work so I had to change to a new model that they provided. So after carefully noting down all the settings of the Fritzbox 7390, I installed and configured the new modem/router (Sagemcom). Everything seemed to go OK except for a few issues. I was no longer able to reach my server from within my network with my duckdns logon and my SSL Expiry Sensor stopped working.

After a little reading and googling, I realised that my new modem/router did not support NAT Loopback. After a further period of investigation, I found a solution to the duckdns access. This involved the following steps

Disable DHCP on Sagemcom Modem/Router
Enable DHCP on Pi-Hole
Create Entry in Pi-hole HOSTS to direct duckdns queries to local address.
Also needed to add an entry in HOSTS for my PIVPN as this was also not accesible.

So now I can access Home Assistant with https inside and outside my network using duckdns. Furthermore, VPN server also works without problem. The only issue remains the SSL Expiry sensor that just will not work.

I realise that my setup has probably grown a little haphazardly, but I would be happy to rationalise the various installations, if helps to solve my current problem.