How old is Franklin,I can't remember if you mentioned that. Does he gape in or out of the tank or both, sand for how long ? They all gape sometimes so hopefully nothing else is going on but it sounds innocent enough since he's not breathing heavily. As for his lack of activity, adult beardies in captivity
are not like the wild ones, they don't hunt, don't need to go far to find a good basking spot or run from predators so they are content mostly to just be comfortable. Other than breeding mode when they can be restless they just don't have much to do so some adults are lazy to a degree. So that's a possibility.