Howdy Rick,
I separated the MISO connection from the MCU. The boosterpack already has an external 3.3k pullup, so I did not add one of my own. The results were identical, probing at the boosterpack's header interface and on the IC pin itself (pin 17).
In addition, I verified that the corresponding GPIO pin 1.7 was functional on the MCU. It works correctly in both the input and output modes.
Are there any other steps I can take?