Like @P3D said, some build platforms have been known to leak. eg:
I’ve seen it myself a couple times. If you send pictures to Support they’ll probably replace it for you.
If you’re using a Form Wash, make sure the fill level is correct and the platform doesn’t submerge past its lip. I recall (but can’t find) a post some time back where someone fixed a leaky platform by drilling a hole in the top side and filling the cavity with self-expanding foam. Silicone caulk may have been tried as well.