Secure conections and systemd-resolved

Not very likely

Then it is a domain related issue - perhaps they have been changing hosting platform and you have been caught up in the changes?

In any case - using systemd-resolved is the better option.

One reason is the increased everyday use of VPN where using systemd-resolved solves a common issue where the resolv.conf is not reset correct when you disconnect your VPN.

It is also easy to switch - only takes a few commands

sudo mv /etc/resolv.conf /etc/resolv.conf.bak
sudo systemctl enable systemd-resolved --now
sudo ln -s /run/systemd/resolve/stub-resolv.conf
sudo pacman -R openresolv