Anchor links to headings not working

After customizing the look of the Table of Contents, when I click on the headings in the ToC of a blog post, it doesn’t jump to the section/achor point. The URL address does change to the correct anchor, for example: when I click on “Third Heading” in the ToC, the URL changes to “https://example.com/blog/post1/#third-heading” but it doesn’t jump down the page. It’s not working on the Desktop (Firefox) nor on the phone. How can I fix it? Thanks a lot in advance!

My wordpress ver. is 6.6.1, theme is OnyxPulse ver. 1.0.2, php ver. 8.2.16.

The page I need help with: [log in to see the link]