Possibly due to https://github.com/python/cpython/pull/4458 (https://bugs.python.org/issue31975) which landed in 3.7.0 alpha 4.
Incidentally, the matrix DeprecationWarnings related to the test
failures seem to have started with the switch of default python3 from
3.6 to 3.7, 21 Nov 2018. Not from numpy as such (certainly not numpy
1.16).
