Ubuntu DNS Resolve Failure Fix
It seems that Ubuntu DNS Cache seems to stop working. The following is one of the easier fixes. More to come...
Check the folder /etc/netplan to see if there are more than one config file *.yaml
If there are more than one, remove the least relivant one and update the other.
Update DNS in /etc/systemd/resolved.conf
sudo nano /etc/systemd/resolved.conf
sudo ln -sf /run/systemd/resolve/resolv.conf /etc/resolv.conf && sudo systemctl restart systemd-resolved