Try downloading nightly version, this past months users (including me) have been complaining about not receiving ads. It first started on Windows and Mac and and now in linux. This is known as “july bug”.
Also this month we have lots of issues, but well, to many issues, to much code to check and to test so it doesn’t create more bugs.
In any case, like i said you can try downloading nightly version if you are desesperate for ads, some users report that in stable version no ads come in but on nightly they do. I can corroborate this, but is not for sure it will work for you, but you can try.