Layer appears and works when viewed in slide-preview mode, but not in scene-preview (nor in publish) mode

Here is the fix from Articulate.  All good!  Thank you.

The reason why the Essay question slide immediately goes to the next slide is because of the Feedback setting of the question. If you have this set to "None," upon submission of your Essay, Storyline will immediately go to the next slide because it is not expecting any Feedback layers to show.

Setting this to "By Question" will generate the built-in Thank You layer, which will be the feedback layer that Storyline will show upon submission of your Essay. Since you have a custom feedback layer, deleting the generated Thank You layer and renaming your customized layer to "Thank You" instead will ensure that this layer is shown once you've submitted your answer.

By the way, I also removed the "Change state to Hover" trigger in your layers because the Hover state in Storyline is already a built-in function.