Can anyone help? Damp patch

[Noodle14]

Hi everyone, I’m new here but hoping someone can help. I’m having a new kitchen fitted and the builders have removed our old cabinets. Under some of the cabinets was a large wet patch on the chipboard sub floor (no flooring was ever payed on top) and I cannot work out where the water is coming from!!
Under the chipboard there is the following. Concrete floor then a gap, then a wooden frame with insulation fitted between the wood. All of this is bone dry. It’s just the top couple of mm of chipboard that is wet. There is no leak from above either. There are some other small wet patches where the old kick board met the ply wood floor.
Would anyone have any idea where the wet patch might be coming from? I’m at my wits end and can’t fit a new floor until we figure out where the water is coming from 🤦🏼‍♀️
Thanks

Should say laid on top not payed!

Is it still wet or old signs of damp?

What did you have as the floor covering in front of your kickboards? Have you mopped the floor in the past and this area is a fraction lower?

If it's not coming from below then it has to be something above or a spill unless it meets your outside walls and is coming in from there?

Thank you for replying! It’s definitely wet and not historic. We have not mopped or spilt anything. The whole kitchen floor is chipboard and it extends under the cupboards. There is a gap between the chipboard and the walls.
One wall is an external wall (end of terrace) which seems damp to me. I was wondering if there’s anyway it could be some form of condensation if we have a damp issue somewhere 🤔

What was above it previously? If it is just wet and not mildewy then suggests it might be quite recent.

What is on the other side of your external wall? No drain pipe, outside tap or anything?

No old fireplace or chimney close by?