If you configured the motion sensor in Hue Essentials, it should still trigger scenes when lights are on. However, it could be that the motion sensor is (temporarily) disabled because there is enough light. So if the lights are on, the motion sensors thinks it is light enough (day) already so it will not activate a scene.
To fix this, you would need to change the daylight sensitivity so the motion sensor is still active when your lights are on. Of course, if your lights are too bright, this will not really work very well.
What you could do instead is only trigger scenes between certain times on the motion sensor. Furthermore, set the daylight sensitivity so that the motion sensor triggers at every light level (even when bright). I think that would work better in your situation.
You can find the daylight sensitivity options under the three dots on the motions sensor configuration screen.
You cannot assume this, as it depends on the light level. It could be that one time it does trigger when the lights are dimmed a bit, but if the lights are brighter it does not trigger. It is on the wish list to make this an option, see the following: Motion sensor - Trigger only when lights are off