Drag and Drop Activity

You didn't identify where your problem was occurring, but I know you will have problems on slide 1.10 with these triggers:

As soon as the learner drops the first object on its correct target, the system  checking routine kicks in. Since none of the layers it uses are present, it advances to the next slide. Since you are using your own feedback layer, and are not sending a score, you don't need to use the submit trigger. Delete these, and use the one you are using on the custom submit button. Go to the slide properties, and deselect Submit button, so a learner doesn't inadvertently click it.

Another potential is represented on the Success layer by this trigger:

The built-in states (like Hover) all have automatic triggers to perform their native functions. If you create a trigger that duplicates that function (like this one) you may have problems. They are unpredictable, so I can't tell you what or when they may happen, but you won't like it when they do. Delete this trigger, and let the Hover state do its own thing.