After an hour of troubleshooting with Prusa Support we could still not get OctoPrint to work on the Pi when attached to the EINSY. Support finally decided to send me a new EINSY board for replacement. (Many thanks to Shane for his help with all this!) After receiving the new board, I attached the Pi and was immediately able to connect to the OctoPi server via a browser and use OctoPrint. All is working as expected! Support said they never saw an issue like this before with the Pi. Recommend you contact Prusa Support for help on this!