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.

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

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

jsfiddle.net/glenthemes/qhjpfs52

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! ☺️