We dealt with the same thing by our front entrance a couple years ago. At first it was just a tiny bubble near the door, then after one snowy season it spread way farther from all the wet boots and slush getting tracked in. I had a few contractors come by and most barely even looked before throwing out a price. The only crew that actually checked underneath and talked about the subfloor was St. Albert flooring contractors. They were pretty straightforward about the cause and fixed it properly instead of patching over it. Haven’t had a problem since, even with kids and winter traffic constantly coming through.