Only a power cycle works to reset

[smbunn]

I have a Pysense with a FiPy installed. It runs beautifully if I cycle power. But if I interrupt my routine from Atom and then try a Ctrl-D or

import machine  
machine.reset()

but neither will restart the routine. It gets stuck in the library function for the MPL3115A2.py routine. I can CTRL-C and it instantly stops and responds. Noting I do can restart my python code except a full power cycle which calls the routine in main.py

Why does power cycle work but machine.reset() not?