Drag and Drop Submit Button keeps reappearing

Hi Captivate community!

This is my first post here, I am working on an E-Learning course with Captivate 11.8.2 (I'm happy to update once this course is done)

Here is what I am trying to achive: 

A Drag&Drop Interaction with 8 drag targets and 8 drop zones. Each drop zone should only ever recieve 1 target (this works just fine). The user should only be abled to submit the interaction once - this does not work. The user can navigate back and forth through the course via buttons. Going back to a previous slide and coming back to the slide with the Drag&Drop always displays the "Submit" button for the Drag&Drop again.

Here are my Drag&Drop Options:

Here are my Drag&Drop Actions:

Success / Failure messages are displayed via JavaScript. Additionally the scripts show and hide some other objects, here is the success script (the failure is the same just with different IDs to show and hide):

window.cpAPIInterface.setVariableValue('_v_quiz_submitted', 1);

cp.show('t_well_done');

cp.show('drop_1');
cp.show('drop_2');
cp.show('drop_3');
cp.show('drop_4');
cp.show('drop_5');
cp.show('drop_6');
cp.show('drop_7');
cp.show('drop_8');

cp.show('content_blocker');

cp.hide('drag_1');
cp.hide('drag_2');
cp.hide('drag_3');
cp.hide('drag_4');
cp.hide('drag_5');
cp.hide('drag_6');
cp.hide('drag_7');
cp.hide('drag_8');

What I have tried as a last resort is to use BrowserInspector to get the ID of the Submit button and remove it by force from the page in a script i run whenever the user enters the slide:

if(window.cpAPIInterface.getVariableValue('_v_quiz_submitted') == 1)
{
    //si21004 is the ID of the submitbutton found in browser inspector, it is always that
    var toDel = document.getElementById('si21004');
    if(toDel)
        toDel.parentNode.removeChild(toDel);
}

This works .. the button is removed from the DOM .. however .. it is still visible:

You can even see the outline of the actual element that is "behind" it shimmering through .. I can not access this submit button in any way. I can't find it in the DOM inspector and I can't select it with any browser tools - yet it blocks my Next-Button visibly.

So - can anyone please tell me how to do this properly? I am sure I am going at this in an overcomplicated way .. surely it is possible to have the submit button only ever show up once and after it is clicked it is gone - right? I must be missing something quite obvious here and I am grateful for any advice 🙂

Thanks a lot in advance!