Unfortunately, FlexLayout is not intended for such use-case.
Due to the features of CSS flexbox layout, FlexLayout has no fixed sizes.
This limitation affects the parent scroll view, as it cannot calculate the size of the scrollable body with several flex layouts. As a result, the scroll will be mishandled.
To avoid any issues, I would suggest you reconsider the current implementation and avoid using several flex layouts within the scrollview.
As a solution, you can replace Flex Layout with a common responsive moving feature.
https://snippet.webix.com/29jop1kn