That dog reaction is what gets me. Animals don't lie about this stuff, they just respond to what they sense without any of the overthinking we do.
I had something similar up here in the Pacific Northwest maybe six years back. My cat wouldn't take her eyes off the corner of the bedroom ceiling for almost three days. Nothing on the roof but the feeling in the house was just... off. Heavy, if that makes sense.
The walking sound is interesting though. Was it rhythmic, like actual footsteps with weight behind them? Or more scrabbly like an animal? I ask because what you're describing with the combination of the sound AND your dog fixating on the ceiling at the same time - that pairing is significant to me. Thats not just a raccoon situation.
Has anything else been off lately? Lights flickering, electronics acting strange, that sort of thing? Would love to hear if others in this thread have had the roof sound specifically. I've seen it come up a few times over the years and I don't think its ever just been "the house settling."