Slide advancing after submitting a drag and drop submit interaction

The problem with the original story is due to two conditions. First, the "Submit Drag and Drop when user clicks Submit" trigger is the first on the list of triggers when Submit is clicked. Therefore, it  does the whole submission thing before it does any of the other triggers. Then having submitted, it doesn't find any feedback layers, so it defaults to jumping to the next slide.You have renamed the Feedback layers so you can use your own feedback, and have written your own triggers to handle the error checking, which is all good, but those triggers are being skipped, and the names of the feedback layers aren't being recognized.

Since you have written all the triggers, and have triggers to show the feedback layers, I wonder if you need to use the built-in interaction.

Move the submit trigger to the bottom of the list, and everything may be well. If not, I would remove the freeform. You may have to add a few triggers to change the dropped items to Drop Correct/Incorrect state, but that's nothing compared to the work you've already done.