Weeks of something moving around up there and you only just set the camera up - fair play for finally doing it though, most people just convince themselves it's pipes or rodents and leave it at that.
What time of night does the movement tend to happen? That's the bit I'd want to know first. Attics are classic transitional spaces, liminal in the same way doorways and corridors are, and there's documented cases going back decades of people reporting rhythmic movement sounds that turned out to have no physical explanation whatsoever once the property was properly investigated.
Had something similar myself back in the mid-90s in our old house in Salford. Scratching, footsteps, the whole lot. Camera footage was inconclusive but the EMF readings up there were genuinely unusual.
Post the footage when you've had a chance to review it, even if it looks like nothing at first. Sometimes you only notice things on the second or third watch. Looking forward to hearing what you find.