re: Slab leak detection - plumber recommendation?

I don’t think it’s very likely water from outside your home is going under your house and causing an issue OP. If it was that much of a leak you’d almost definitely notice it outside.

My parents had a leak under their master bath bamboo wood floor. It was a pinhole leak in the copper supply and crazy thing is it was the hot water and it made that spot noticeably warm through the slab and flooring. They ended up paying a plumbing company $400 per fixture to re run pex through the attic to their entire house.

Without knowing more of your specifics it’s hard to pinpoint, but if that’s a remodeled area I’d certainly 100% eliminate anything related to that under the slab.

You could turn your water off and bring in water from the outside (pool in buckets) and dump into the sinks/ drains and see if you are getting moisture from a sewage line?