Nb sticky headers disappearing when they shouldn't

[Yoyokrazy]

          Tested on Windows 11.

Yep, I also found it confusing as to when a sticky header would appear.
Scrolling through woooooo.ipynb in the testing repo, I had to scroll several times past ### Sec before it would appear in the sticky scroll UI.
I would have expected the header to be displayed right after it scrolled out the top of the view port.
I also saw that headers higher in the hierarchy such as ## other header would disappear and reappear. Shouldn't the H2s remain as the H3s change?

Originally posted by @gregvanl in #188728 (comment)

[Yoyokrazy]

Somewhat related to visible range issues and multiple md cells with headers in a row.