How old is Finn now? Is this new behavior? While it is true that many greyhounds love their walks, even when they get old and infirm, sometimes, as they get older, they decide that walking is overrated . If he seems fine otherwise and he doesn’t have to be walked for potty breaks, I would let him decide whether to go or not.
It actually sounds like a combination of things. Like something spooked him, probably something so weird or minor (to you) that he connects with morning walks on certain days, and since walking was becoming less of a priority for him, he decided, nope, not this time. As I am sure you know, they can have strange, quirky thought processes, that’s one of the reasons I love them