Please set up a reduced test case on CodePen – so just the HTML and CSS for your menu. I bet if you do it this way you’ll find the issue.
That said, I don’t know why you have a “normal” and “responsive” CSS file as it’s not a good practice.
In looking at what you’ve got, you’re dealing with over-complicated markup and CSS. So if you simplify it down to just your menu, I bet you can find the problem.