Speed of the website, adsense suggestions

Greetings for the day!
Adsense has been my source of income since 8 years. I have multiple websites. My ads on this URL indianplayschools.com stopped showing. I have sub-domains on the same website each is loaded with different wordpress set up. I got no notification. I am able to see ads in the sandbox test by posting this URL here http://ctrlq.org/sandbox/
Other sub-domains with missing ads

The ads are running on other domains with same adsense account

I have checked everywhere on my adsense page, I checked status and it clearly says
You have no account-level policy violations on record. Thank you!
You have no site-level policy violations on record. Thank you!

I have checked with my hosting provider as this website is hosted on different server , but they say that no changes have been made from their end.
Can anyone help me on how I can get back my ads?
I think speed matters. When I try to add ads using Google official plugin, I sometimes manage to confugure(though they are not displayed) and sometimes it asks me to try again as the response of the site is slow. The hosting providers say that it is my design issue. But, I am totally unaware
Please let me know how I can get back ads. Can you suggest any plugins which will boost my speed. Do you know any other reason why the ads suddenly vanished from the whole domain.
Please help. Thanks in advance.