Viewport delay prevent quicklink for above the fold

Hi there,
I'm experimenting with this module on a site with about 300 pages and not a huge amount of visitors.
I tried to add a Viewport delay (tried values 20–500ms) to prevent prefetching content which appear only briefly on the screen.
When there is another value then `0` links which directly appears on screen on the initial page load are not processed. If I scroll and other links appear on the screen they started to be processed. When I return to the top the previously unprocessed links got processed.

Is there some settings I overlooked or is it a bug?