Hi Matt,
apt-cache policy systemd
systemd:
Installed: 229-4ubuntu21.15
Candidate: 229-4ubuntu21.22
Version table:
229-4ubuntu21.22 500
500 http://archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
229-4ubuntu21.21 500
500 http://security.ubuntu.com/ubuntu xenial-security/main amd64 Packages
*** 229-4ubuntu21.15 100
100 /var/lib/dpkg/status
229-4ubuntu4 500
500 http://archive.ubuntu.com/ubuntu xenial/main amd64 Packages
where it is reported 229-4ubuntu21.22 as candidate version while the fixlet is trying to install the 229-4ubuntu21.16 version.