The Kepub Output, Kepub Input, Kepub Metadata Writer and Kepub Metadata Reader plugins and the KoboTouchExtended driver all share a lot of code and structure. They are all failing with calire 5.1.0. I have put a beta of KoboTouchExtended driver
at the end of it's thread that I fixes it here. If that solves it, I will look at the other plugins.
But, the 5.1.1 beta also fixes it, so that might be the better route.