Yellow mesh material in slab foundation cracks

We recently purchased a home in central Florida, built in the late 80s, a stick-built home on a concrete slab. Today I noticed a small uplift and depression through the carpet.

Touching the carpet, there’s a faint scent of vinegar, and a moisture detector did pick up a point with moisture. Due to where it is, I’m not able to easily pull back the carpet to inspect it, but I was able to lift an edge and stuff an endoscope under it. What I found was what appears to be a crack or hole in the slab, with a yellow material with a mesh pattern in it. My understanding is that there are barriers underneath slabs, but this only appears to be a quarter of an inch under the surface. There’s also no broken material near it as far as I can tell, making me assume this isn’t a recent development.

What is this yellow material? Why does the area near it smell like vinegar? Should I be concerned?