It may be small consolation but initial tips are as follows:
The dynamic scaling on SN was meant to be run in landscape on mobile devices. I recommend surfing SN in landscape mode and become accustomed to it that way.
I don't spend a great deal of time trying to make adjustments so that it's ideal on every phone because it's just not possible. Not only do different phones treat webspace differently but the browsers themselves also treat web spaces differently.
Some of the choices made about what content to show and what content not to show on a given amount of available desktop space, are compromises. We chose settings that seem to work for [most].
The problem you are seeing in portrait mode with the main forum menus is due to the minimum size of the images used to mark those forums. The image sizes were chosen so that they are [smaller] than the commanded size of the menu item but large enough that they're not fuzzy at that commanded size. What you are running into is a minimum. You might have noticed that everything scales correctly in landscape mode. It's because the image size of the background is no longer the minimum required to scale everything equally.
In other words: In your specific case, there's not enough desk space to display everything in portrait mode since artifacts themselves can not be "word-wrapped" (so to speak) to the next available row.
Cliff Notes: Turn the phone sideways for large menus and drop-downs. The reason you're registering the click and not getting the menu is because your particular browser/SN/Dynamic Scaling/desktop resolution combo said, "Nope... not enough room".
I tried a couple of different browsers and some handle that issue differently. None of them crashed though
That's a plus.