Header Background Image flickers when loading

Here are my sites . https://www.tom-abraham.com/ and https://www.sabrina-abraham.com/en/. In both site when loadind and when switching to different language background image flickers . I have enabled parallax effect and background attachment is set to fixed,background position is default, background repeat is no-repeat and background size is set to cover . I have built the site using elementor plugin and ocean wp theme . Can anyone help me fix this issue?

I think it might be caused by a recalculation of the JavaScript that dynamically is setting the CSS (like height and width) on the background. Not sure what the best solution is, but if nothing else maybe you can add a Preloader plugin that does a fast fade in on page load.