I check up your site and It seems that, the issue(jump to top while scrolling) occur by custom css, which are conflicting with patent css, so that element does not able to load clearly and issue occur.
Please check the custom css and fix the issue. Here is step of checking css conflict issue:
=> first backup the custom css(copy in other backup file) and check the site. and you check 2 step :
1. If there is still issue in site then its not css conflict.(check for other issue like Plugin/custom jQuery etc)
2. If there is no issue withuot custom css, then it means there is conflict on css.
Now Here is step to remove css conflict issue:
=>Add custom css one by one step and check the site and similarly go on. While you find issue in css then remove that code.