So I eventually solved it. There seemed to be some sort of incompatibility between the Tensorboard and TensorFlow versions. I can’t remember exactly what I did to resolve the issue but I ended up either matching the two versions (e.g., both nightly or both release), or sticking with the latest nightly build of TensorFlow and the latest stable release package of Tensorboard. I believe that initially, I was running an older nightly build of each and there was some sort of incompatibility.