The first floor of my home is orange oak pre-finished engineered wood planks glued down on concrete slab. We've been in the home since 2013, the floor probably dates back to the 90s or early 00s. We have not previously had any trouble with the floor other than normal surface wear and tear.

About 10 years ago we started using our spare bedroom as a home gym. I put down a layer of interlocking foam tiles, then an 8x10 rug. The foam made for a comfortable workout surface, and I expected it would protect the wood from dumbbells set down roughly.

Recently I felt an odd bump under the rug, peeled back the layers, and found that my flooring was a mess. The bump was a raised "bubble" where it feels like the veneer layer of the planks had delaminated and lifted. Elsewhere, the factory finish looks very rough, almost blistered (but thankfully not coming up), and the oak is darkened in a pattern that looks like the square spaces between the foam joints.

To my amateur eyes it can't be anything other than moisture trapped by the foam tiles.

The home is in San Diego where we don't get that much rain and we've had hardly any in 6 months, and the room is on a side of the house with gutters and no drainage problems. So I struggle to understand why there could be so much moisture coming up through the wood floor. I did an overnight water meter check and there was no flow detected, so there is no high-volume slab leak, though I suppose this doesn't rule out a small dribble. I have no idea where or if there are pipes under this room.

We took up the rug and tiles, and we are going to keep the room warm and watch to see if the dark wet look fades in the boards. We would like to salvage the wood floor and eventually return the room to being our home gym. I have questions!

1. Does this have to be some kind of leak? Or can normal slab moisture cause this much trouble when trapped under 80 sqft of foam tiles? (Remember this is ground level in SoCal, not a basement or somewhere really damp).

2. If I wanted to rule out a slab leak, who can do that most effectively? Plumber? Flooring contractor? Engineer?

3. It really doesn't feel like my entire planks have warped up from the slab, it feels like the veneer layer delaminated from the plywood and formed a very flexible "bubble" that I can flatten with my hands. Is this a known possible failure for engineered planks? After giving the floor sufficient time to dry out, could I bore some small holes through the veneer, inject some glue, and smash it flat under heavy weight to cure? What adhesive?

4. Again, assuming the room appears to dry out and we can repair the bubble well enough, what can I do differently when setting it up as a gym? I assume any large foam or rubber mats will cause the same vapor trapping issue. I've thought about alternative padding like cork or felt under the rug. Would 1/2" of cork or felt hold up, under a rug, with light home gym usage? Is cork permeable enough to alleviate the current moisture challenge? Or would I be inviting a new issue with mold growing in the cork? Would felt be dense enough to protect the wood from a dumbbell set down a little too hard?

I would love to hear opinions and ideas, especially from anyone who has seen similar effects from using foam tiles like this.