My original thought was that it was a problem with firmware and OS level, and that I cleared that up when I upgraded the Pi3B. Then the problem came back. The same firmware and OS are running on another Pi4, I just don't have physical access to it right now. I'm going to try to find another Pi and swap the BerryIMU-GPS to that and see if the problem follows. I'm also going to look and see if one of the solder joints might have been compromised.