That’s probably what’s going on. I have no idea why Smart Lighting is failing this way, other than the numerous reports here about it.
One work around is to use Smart Lighting to turn on the lights from motion, and my little app called “Turn off after motion stops” to turn them off later. My app doesn’t have the bug. This would hopefully be a temporary workaround, until ST fixes Smart Lighting. See this thread: Turn off after motion stops.
Another way around ST’s bugs, it to use my Motion Lighting app: Motion Lighting