The Keystone website has a 3D walkthrough of your trailer. They show two floor vents, one directly in front of the sofa and one centered on the kitchen floor. Both are positioned "long side toward the slides.
You can access the 3D photos here:
https://www.keystonerv.com/toy-haule...03-toy-hauler/
I'd suspect that if the factory "forgot to cut out a vent" there would be no airflow in that area (no hole) and if they cut it out and failed to cut the vinyl, you'd easily be able to locate the problem with a simply "fingers over the floor" until you find the depression under the vinyl.
One possibility is that one of the floor vents is not secured well to the floor and there is some airflow around the vent, under the vinyl and causing the vinyl to billow once it warms up enough to be flexible. The vinyl is not glued to the sub-floor. I'd urge you to resist the temptation of spreading glue under the vents to prevent billowing. As the seasons change, the vinyl expands and contracts, gluing it to the floor could cause it to split, a problem in many trailers about 10 years ago.