when trying to submit both a video and attached file it will only submit one or the other never both at the same time.

You will need to save the video to your computer. To do so, click k on Studio, then click on your video to view it.
Then click on the 3 stacked dots in the upper right corner and click on download. Save it to your computer. After doing this, you will attach the video just like you do your file(s) in the submission area. You will submit everything together thru the Files option.
You won't go to the Studio tab anymore.