Judging by where the stain is on the floor I think it is safe to assume you have a water leak. Cannot tell if from the pan or the curb. Do you know how the whole shower was installed and products used? Installer still around as you may want to have him back to look at it. But you will more than likely need to have some selective demo done in my opinion, but definitely get someone in to look sooner rather than later as you do not want the wood to start to rot or develop mold.

Not a leak it’s hot mopped and fully sealed, the drain line is 2 feet away and 1/2 foot high. It was fully inspected and water sat in the tray for 48 hours. We have video and pictures on the entire process.

Sorry tray is 1/2 foot higher than this part

Better view of shower and curb.

That's a leak. Zero doubt. It’s water saturated, and the iron inclusions are rusting.

"Not a leak it’s hot mopped and fully sealed"

The spot where that is showing would realistically only come from one thing, water. Is the "curb" pitched properly? Is it leaking from under the door?

May be leaking from
Under the door or when the door is opened and dripping.

@celadon was right. We did shower pan tests held the water no issues and finally last night, I said it has to be a leak. So husband annoyed with my constant complaining about it filled the tray up to the top of the curb - low and behold a leak. Contractor has moved out of state - no come back with them. I have their COI and license information but nothing much use now if the business is no longer here and insurance expired. Pretty gutted about the whole thing. We think it’s the top of the curb. I have pictures of the build that I can share, if anyone can help with advice. Hoping I can repair the curb as we don’t have money for a full redo of the shower but fear the answer is no.