Do not assume that they are "self adjusting" brakes. Most travel trailers do NOT have self adjusting brakes. The brakes need to be adjusted upon delivery (hopefully, your dealer did this), and then every 3,000 miles or anytime you detect decreased braking activity.
There are other possible problems that can cause poor braking performance on a new trailer.
There could be an electrical problem which is causing one or more magnets to not activate. Like mbopp recommends, check the brakes to make sure they activate. You can jack up each tire, and then apply the brakes through your tow vehicle controller or by pulling the break away pin. If the brake(s) don't activate, you'll need to find out why.
Another issue some folks encounter is grease leaking past the grease seal and contaminating the brakes. For what ever reason, this seems to occur mostly on newer units. The only way to positively tell if this is happening is to pull the brake drums and visually inspect the brakes.
Jim
2016 Ford F350 Turbo Diesel SRW 4x4
2017 Grand Design Reflection 297RSTS
2013 Ford F350 Turbo Diesel SRW 4x4 (Destroyed by fire - 8/29/16)
2014 Grand Design Reflection 337RLS (Destroyed by fire - 8/29/16)