Side menu disappears

Question

Google Chrome	Microsoft Edge	Windows 10 Home
version 98.0.4758.82	version 98.0.1108.43	version 21H1

If you scroll down the page and hover over any link, the side menu disappears when you return to the top of the page (Figures 1 and 3). The disappearance is also observed in incognito mode (fig. 2).

The phenomenon is detected by scrolling down to the words "Hire a developer" (you can go lower, but not higher). The menu does not change its distorted state until the pointer is moved, but if it was on a left-sidebar item, the state will change when you leave it. The menu items do not disappear smoothly, but in whole lines (first the word Home disappears entirely, then PUBLIC, etc.).

The change can be observed even without authorisation, but it requires removing the top bar (fig. 4) (via developer's tools or by using a standard cross). The selected menu item disappears one by one: first the text and then the background (fig. 5).

Presumably, the minimum page height should be 4814px (matching page). But this is not only true for certain question pages, for example the general question list (50 questions per page) (Fig. 6) or the synonyms page (Fig. 7) are also subject to this change.

It is found that there is a minimum page scrolling speed. If the speed is insufficient, the menu will remain visible. It's also possible to get to a state where you don't have to remove the cursor from the link (fig. 8).

Figure 1. Side menu disappears	Fig. 2. The problem persists even in incognito mode	Fig. 3. It is even possible to hover over a link in the same block	Fig. 4. Top panel of the unauthorised user

Figure 5. Intermediate state of disappearance	Fig.6. General question list	Fig.7. Synonyms page	Fig. 8. Interesting result

UPD

Laurel was able to repeat the phenomenon on Skeptics Meta using Google Chrome on Mac:

Answer 1

I managed to reproduce it intermittently (on Windows using Chrome, Brave and Opera GX; no repro on Firefox) on different SE sites — the first time I noticed this was before this question was posted.

The code below may help to repro on a specific page, I think the issue is both related to the scroll-up speed and to the page height. Sometimes the bug doesn't happen, so I refresh the page and try again.

Type this once on your browser's console (press Ctrl + Shift + J or Cmd + Shift + J to open the console):

function scrollBug(delay = 0) {
  scrollTo({ top: document.body.scrollHeight, behavior: 'auto' });

  setTimeout(() => {
    scrollTo({ top: 0, behavior: 'smooth' });
  }, delay);
}

Then just call the function with scrollBug() to test.

When I scroll manually, sometimes all links are hidden. Using the script above, only the first one is hidden.

It's worth mentioning that my window.outerHeight is 864px, so the script may not work if your resolution is too different.