More bad news regarding Affinity Designer 1.6… The latest update no longer opens SVGs generated by boxes.py correctly. 
Verified this on two Macbooks on two OS versions (Sierra and High Sierra).
Running through my library of SVGs generated by a variety of programs shows that across all programs and online generators, many files that were previously displayed correctly no longer show up at all (other than an insanely large boundary box) and/or are “missing” layers previously accessible.
Still characterizing this for a bug report to serif, but thought I’d share with the group – you may not want to update your AD quite yet…