Hi @ilya, the issue might be caused by the two embed widgets you have on your page. Those embed widgets are loading iframes that are trying to load a page that does not exist, and when the 404 page not found displays, it seems the flicker occurs.
One thing I might suggest, is to make a duplicate of your site, then remove the embed widgets and test if you still get the flickering.
Also which elements specifically are having the flicker? Which text elements and links ? Which browser are you using?
Cheers, Dave