Page jumps on scrolling

I am having trouble fixing the issue. The page jumps when scrolling downwards or upward. I tried making the position of the header to absolute but then the sticky header doesn’t work.

Link to the website:

• This topic was modified 4 years, 2 months ago by ak45.
• This topic was modified 4 years, 2 months ago by James Huff. Reason: redundant link removed
• This topic was modified 4 years, 2 months ago by James Huff.

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