Adsense Ads are Not Showing Sometimes

Question

We have an application developed with WordPress and Adsense Ads are displayed with the Google code. Sometimes it do not work properly. Sometimes advertisements are displayed and sometimes not. When we looked at the source code of the site, we saw that the ad was always loaded into the Iframe, but the inside of the ad was sometimes empty. Sometimes the ad starts to appear when we refresh the same page. We observed that there was an inconsistent situation. Does anyone have any previous experience or knowledge on this subject? I would appreciate it if you could help. Thank you so much.

You can check the ads on the following link. https://youtubethumbnaildownloaderonline.com

I tried to optimize the current code by placing the first script code in the header and , second two parts where ads are placed below Nav bar.