Slideshow in a Slideshow Question

Hello! I am working on a graphic design portfolio website, using HTML, CSS, and Javascript. The format is pretty straight forward - I am using a multi-drop down menu to categorize my work (similar to this: The work category opens up to a list of general areas (logos/branding, posters, my thesis work, etc.). Each of the general areas opens to contain a slideshow of images/descriptions, I am naming them “mySlides(x)”. These are working great. Each project has a representative image, title and description.

Next, I am trying to add a secondary slideshow of images, for projects where I need more than one image displayed. Basically, a slideshow within a slideshow. for which I am using the naming conventions “SubSlides(x)” . I’ve been able to write it out and the result is close to flawless. The ONLY issue I am having, and can’t find a similar issue anywhere online, is that when a SubSlide starts, all images are displayed, instead of just the first. Once I press the next/previous buttons assigned to the SubSlide, the slideshow reacts normally. I’m not sure how to solve this, any suggestions would be great.