That xxxxxx/m/xxxxxxx.html
and xxxxxx/mobile/xxxx.html
These are not UBB.threads style pages. Either Google is attempting to crawl pages that it found in a discussion on your site where "example urls" were talked about. Or you have third-party software who've created those links. Or the google webcrawler is overzealous and is attempting to find pages with your domain name, created by a "web monitoring" / "seo status" site (for example, "link-assistant dot com" or "semalt dot org")
As for your second post, unless you have "viewport" declared within the header of your indexed pages, they all will get flagged in GWMT's "Mobile Usability" section for not having it in there. If your pages are not mobile-friendly, a standard viewport entry will probably do more harm than good for your website's mobile device users. Beginning with version 7.6.0, UBB.threads will be mobile friendly.
Lastly, with the stock urls that were introduced within 7.5.8 (fixed in 7.6.0) you will have all sorts of errors in the Google Webmaster Tools. A lot of things are being put in the URL that are not supposed to be there. Stock 7.5.8/7.5.9 URLs are quite bad.
https://www.ubbcentral.com/forums/ubbthreads.php/topics/255500#Post255500
