Long sidebar jumping issue

[glenthemes]

Hello, thank you for creating this plugin, it's worked smoothly for the most part when the viewport is the window/document. However, long sidebars create a jump when the viewport is a specified element.

Please note that in the following demos, the top bar's height is 100px and the top gap is 20px.

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[1.] Default viewport (window/document), working great ✅ :
jsfiddle.net/glenthemes/p3ejo8u1/

Screen.Recording.2024-09-18.at.9__65pct_smaller.mp4

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[2.] Specified viewport (custom scrollable element), has a jump ❌ :

jsfiddle.net/glenthemes/qhjpfs52

Screen.Recording.2024-09-18.at.8__75pct_smaller.mp4

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Interestingly, scrolling down and sticking to the bottom seems to trigger this issue, and scrolling up has no issue.

Any help or advice is greatly appreciated, thank you! ☺️