There seems to be a bug somewhere in the CVS version of
> matplotlib or the 2.3 version of agg that's causing me
> sporadic segfaults. It's possible this isn't general
> and is due to some other compiled code but doesn't seem
> particularly likely as the bug didn't appear when
> running with a copy of matplotlib from CVS on April 14.
> However, I've no idea what's causing but problem and
> this may be a coincidence.
Compile mpl with VERBOSE = True in setup.py which will help inform
where the segfault is occurring. You will want to rm -rf your build
dir to force a clean debug build.