I just saw my problem might be related to this one https://community.ipfire.org/t/after-update-to-core-141-no-more-pakfire-list-availble/1378/
The temporary work around to proceed with the upgrade from 142 to 144 is to add the DNS server IP to /etc/resolv.conf like I have done. Seems that etc/resolv.conf will be regenerated at reboot.
Let’s see if the upgrade has solved the issue (I can only reboot tonight).