My OS : Mac OSX 10.14.6 Mojave
MyEnv : python ==3.6.9, python==3.7.6
both have numpy==1.18.1 installed
each env fails with Illegal instruction 4
The cause is numpy. To verify open a python session in a terminal and import matplotlib or import pandas or import numpy and the session may quit if you have this problem.
The solution for me :-
For python==3.6.9 I installed numpy==1.16.5
For python==3.7.6 I installed numpy==1.17.4