By switching the Nova sidebar to the left, the page breaks out of the wrapper on forum_list, when viewed on mobile (Samsung S6).
Took a while to find the problem, but tracked it down to the sidebar on left eventually.
It may be something else going on, I can't replicate that issue on the default nova with a left sidebar. When you say it goes out of the wrapper, do you mean you can scroll to the right in a mobile device? Or something else going on.
The categories break out of the wrapper and yes you can scroll right.
With sidebar right, it works ok. Ive tried with the unmodified version and its the same.
360 x 640 using code inspector in Firefox, equivelant of Samsung S5 / S6 mobile.

Yes it does. :(

So you may have some responsive settings on your ad setup.

Maybe try placing your entire div code inside something like this:

<div class="extraContainer">all your ad code here</div>

Then some CSS in extra.less:

.extraContainer { display: block; overflow: hidden; }
OMG, how the hell do you learn this stuff! Thats sorted it.
P.s. I just used the same method in a custom page, as the following alert box also broke it.
<div class="blockMessage blockMessage--error center">
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