On smartphones, there is a click instead of a scroll. Why?

Question

css

I scroll through the site on my smartphone. I scroll slowly and, if I tap on the menu bar, then instead of scrolling further at this moment, there is a click and the menu unfolds. If scrolling is done much faster and also sniping into the menu, then it will not unfold and the site will scroll further.
Of course, the point is not at all in the menu, especially since, for example, in the product card there is an increasing picture on which, if you get a tap when scrolling, then the same effect. iOS, Android - everywhere the same effect.
A site on the prest, with kilometers of css, a bunch of js from third-party modules, and in general a zoo. Done not by me. I just had to figure it out.
Give me an idea of ​​what might be. Played with z-index, positioning, nothing helps.