Make sure this Ad works on other places, this maybe Ad configuration issue, put it in other place and test it (not in wpForo Ads Banners). if it works fine on other places, leave a screenshot of the edit Ad screen with Ad editor to allow us check the issues. Are you sure you use the Text mode of the rich editor?

Also I recommend use it w/o spaces:

<script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script>
<!-- eGPU.it adattabile -->
<ins class="adsbygoogle" style="display:block" data-ad-client="xxxxx" data-ad-slot="xxxxxx" data-ad-format="auto"></ins>
<script>(adsbygoogle = window.adsbygoogle || []).push({});</script>

<script async src="//pagead2.googlesyndication.com/pagead/js/adsbygoogle.js"></script>
<!-- eGPU.it adattabile -->
<ins class="adsbygoogle"
style="display:block"
data-ad-client="xxxxx"
data-ad-slot="xxxxxx"
data-ad-format="auto"></ins>
<script>
(adsbygoogle = window.adsbygoogle || []).push({});
</script>


Forums are selected and I've choose top, bottom and reply list to try