Well there are a few things that it could be.
just cuz they used a sealer does not mean anything.
if the floor was put in correct and lets say it was.
there could be a water leak in the pips in the floor.
now there are 2 ways to find out if its leaking.
first find you water meter outside.
AT NIGHT before you go to bed take the reading off it.
lets say it says 75683.2 if the leak is small and im sure it would be the 2 is the number you need to watch very closely.
go to bed do not use any water what so ever.
in the morn check it if it moved to 3 or 4 then that means you have a leak somewhere.
the problem is with this if you WC (toilet) has a small leak or a faucet is drippin then it will cause it to move also.
to fix this problem if you know 1 is leaking lets say the WC shut the valve off under the WC same with the sink and so on.
2nd way is to call someone out that checks for leaks.
I have and use several different ways to find out thses problems. some will listen for a leak some will use other ways.
Now it could be the drain line if the pipe is broke or leaking underground it can cause this.
((you could use dye but this takes a long time to soak into the wood to show up. and if its taken a long time for the water to come up this would not help. But if you call someone they could find this out also.
Now for the BAD NEWS>
you cant let this go on it will ruin the rest of the floor in time. You might have to call a floor guy out to remove only that section of floor to find out the problem and go from there.
If you have any other info you think of that you didnt list here e-mail me and I will help you out.
I have been in the field 20yrs and have done several of these they all have there own little twist so if you need help drop me a line