S2B Pro does not but S2C Pro does throw invalidOperatingModeException

Trying to swap out an ancient S2B Pro radio for a new S2C Pro radio. Used XCTU to establish identical function set, PAN, baud etc. New radio works fine on XCTU. When deployed on Raspberry Pi3B using Digi’s Python3 XBee library under Python 3.5.3, new radio throws invalidOperatingModeException:_Could_not_determine_operating_mode when attempting to execute device.open(). (of course the old radio does not throw any errors.) Why? What to do?

Old Part No: XBP24BZ7PIT-004-revF
New Part No: XBP24CZ7PIT-004-revF