Have you confirmed that Googlebot is being redirected as well and it's for sure a 301 redirect?
If the redirects are IP based, it's possible Google figured out that there is an IP redirect (which is NOT recommended) and therefore, for a brand search, are giving the main domain with the US content - which is all they can see with an IP based redirect.
For your third question:
- Stop the redirect. Use a JS prompt to ask people to set a location preference and set a cookie based on that.
- Use sitemaps to push all country content to the SEs.
- Think about a responsive site rather than an m.domain.com - but if you must have that, make sure to make a separate sitemap for that and claim it in Webmaster Tools.
- Ensure that your mobile content is marked up correctly and if needed, the right canonicals are in place.