My guess is that your floor is installed on a grade level concrete slab, as that is how most homes in Florida are built. If that is so, then what you have there is a stress crack that follows the stress crack that occurred in the slab below. It will only get as wide as does the stress crack in the slab.

Is this over wood framing or slab on grade SOG ?

We're SOG--thanks!

Should have used a crack isolation membrane originally.

Tear out the offending areas and put a crack isolation membrane in. The only problem is that most of them are thick and THAT can cause a height problem. My "Go To" answer is "Greenskin," which is only about as thick as a dollar bill. I've used it extensively and, as a "Peel & Stick" membrane, it's good.

If the link only sells far more than you need, try going to johnbridge dot com and see if anyone has a small quantity to sell/give you. I might be able to help....

Here is a link that might be useful: Greenskin