Welcome to the forum. It is difficult to diagnose any structural problems through a single post on a forum. What you describe may be normal or it may indicate a problem. Have you discussed this with your dealership? Have you walked in other similar models at a dealer's lot to see if they "feel similar or different"? Have you looked at the structural diagrams contained in the Sprinter brochure to see if you can "put 2 and 2 together" ?
You can view and/or download the 2017 Sprinter brochure at:
http://www.keystonerv.com/media/3092...ec2016_web.pdf
On page 14 is a "cross-sectional diagram" that depicts how your Sprinter is constructed. There does not appear to be a "floating floor" but rather a "dynaspan, one piece 5/8" floor" which is laid over a subfloor that is constructed of 2x3" aluminum floor joists on 12" centers. This is a typical floor/subfloor construction technique for "standard weight" fifth wheels.
If you bought your RV recently, as you indicate, I'd urge you to return to your dealership, go inside other similar floorplan models and see if you experience the same "sinking feeling" in those trailers. Then, whether you do or don't feel the same type sensations, discuss the situation with your dealership's service manager and gain answers to your concerns.