Why does google ads steal focus when opening a site on the mobile version of google chrome?

Question

iPhone

Essence: There is a site, it has Input, as well as ad units. We open the site in the mobile version of google chrome and on the Iphone. During the page load, when the html has already loaded, click on the input, after that the input becomes in focus and the mobile keyboard appears. But then mysticism happens and the focus is removed from the input. We press again, it is removed again and this will be repeated. Of course, if you wait until all the scripts are loaded, then this does not happen, but the essence of these scripts is not to interfere and not make the user wait, right? Right. So, in the course of hellish torments, it was possible to establish that such a glitch is due to advertising, because if you remove it, then everything is ok. And the question is, why? Those. why can this happen, why does advertising take over the focus, how to fix it?