HELP! Discolored/SPongy floor! 16 Denali

Check the toilet. The seal, the valve.
If you have a black tank sprayer, that could also leak if its routed at the bath location.
If you have an access plate to see the plumbing for the tub/shower, remove it check the drains.

I recommend get to the dealer yesterday and at least get a complaint on record. Hope you can get Coachmen to fix it. That sounds really expensive.

First thing to figure out. Is the water coming from outside, is it a plumbing leak or a shower stall leak. Simple way to figure out if it is a plumbing leak is to have some water in your onboard tank and turn on your pump. It should run for a few seconds until it pressurises and then shut off. Sit in the trailer for a half hour, look at your phone or whatever. If the pump cycles back on you have a plumbing leak. If not and you do not shower in the trailer you know it is coming from outside. If you do use the shower turn it on and look for water leaks around the shower.

A spongy floor at six months and you didn't run to your dealer for an inspection and possible repair? Oh my.

You've obviously had a leak. If it's still under warranty, I would get it to the dealer right away.
That will be a lot of work to fix.