I've only noticed this issue when making nodes and executing them from Flight Plan. It sits waiting to turn but doesn't seem capable of actually turning the vehicle, so nothing happens. Once I was sure I got it working again by opening Maneuver Node Controller and deleting the existing node, then creating a new one, but I've since been unable to recreate it.
For the record, @cfloutier, K2-D2 is amazing and lets me enjoy KSP the way I like to, so thanks for all the work on the mod!