I had the same issue with the fastboot install route when I tried this for the EFCT16 Software workshop. In that case I first downgraded from 1.5.1 to Open 16.06 (which is listed on the wiki as having been tested). So it’s not directly related to the version, though it could be that something was changed when 1.5.1. was installed that is not undone by flashing Open 16.06.
The TWRP route worked perfectly well.