@MaMu https://bugs.launchpad.net/ubuntu/+source/dnsmasq/+bug/1501189
That appears to be your issue, it’s a bug in dnsmasq/resolvconf where it changes your resolvconf to use 127.0.0.1 as DNS when using port 0 which of course breaks your DNS to external websites. Well, I say bug, but really that’s it’s intended function since they think you don’t want any DNS at all when using port=0.
You can try his suggestion of
Sample implementation code, to be inserted before if [ -x /sbin/resolvconf ]: (in the file /etc/init.d/dnsmasq)
grep -qr port=0 /etc/dnsmasq.d/ /etc/dnsmasq.conf && return
Which should check if port=0 is defined anywhere and if true will ignore the following part so it doesn’t alter your nameservers in resolvconf.

