Running the install for SCCM Current Branch (1702) and the Prerequisite Checker was failing on an issue with admin rights on the target SCCM Site Server. This one was really annoying as I had double-checked everything before running the installer.
The appropriate accounts had been given admin rights to all the SCCM Site System Servers using the Restricted Groups Active Directory Group Policy setting (under Security Settings, under Windows Settings, under Computer Policies) . The SCCM server had not been restarted since the policy was applied.
Restarting the server fixed the issue!