Three nights in a row is the bit that gets me - random one-off sightings I can usually wave away but a pattern like that suggests something is either trying to get your attention or it's genuinely attached to the location rather than just passing through.
Had something similar in my old place near Street, kept catching this dark shape at the top of the stairs and my dog refused to go up there for about a week. Never did get a solid explanation for it.
Did you notice if it appeared at the same time each night? That kind of regularity is actually one of the more compelling details in these reports and people don't always think to clock it. Also worth noting whether the hallway runs north to south - sounds daft but theres a fair bit of anecdotal stuff linking corridor orientation to residual activity, especially in older properties.
What's the building's history like? Anyone else in the house see it?
