With radon mitigation there should be no gaps, they all need filled with silicone or polyurethane over the entire basement. That is critical for the performance of the system.

Is this gap just from concrete shrinkage of the slab, or has there been an interior french drain system installed (so there is a 'waffleboard' sticking up in the crack)?

* Pics

When we bought the house, as part of the negotiations, they had a Radon mitigation company come in and install a radon mitigation system. In the corner of the basement where the radon pipe goes down through the slab, they filled that gap about 2-3 feet out from the corner, but that's it. They filled it with some kind of grey foam, picture attached. It doesn't seem like there is a waffleboard sticking out or anything for drainage.