Comment 56 for bug 1670959

For other souls facing this "Medium" issue,
a hammer-ish workaround that works for me:

1) Run:
apt-get install cpulimit

2) edit /lib/systemd/system/systemd-resolved.service:

2a) Comment out:
#Type=notify

2b) Replace line (may want to remove the -k to let cpulimit throttle it):
#ExecStart=!!/lib/systemd/systemd-resolved
ExecStart=!!/usr/bin/cpulimit -f -q -k -l 50 -- /lib/systemd/systemd-resolved

3) Run:

systemctl daemon-reload
systemctl restart systemd-resolved