Possible bug with scene transition

I'm using a Scene Transition app (In Groups & Scenes) to switch some lights over to evening scene from day scene. In RM, I'm turning on the Scene Transition switch device (created by the Scene Transition app) to trigger the transition. It works exactly as I want it to. But, I've found that I have to turn the Scene Transition switch off again in order for the the transition to happen the next time the rule is triggered. When I turn the switch off, I get this error message:

Everything appears to be working fine. The transition triggers as expected. But I don't think it should be throwing this error.