Not my main area but I do find the railroad connection interesting. Old rail lines often follow really ancient routes - paths that were used for centuries before the trains ever came. So is it the rail line itself attracting something, or is it just that these corridors cut through remote terrain that doesn't see much human traffic?
Cumbria has loads of disused rail lines and I've heard a few odd accounts from walkers around the old Stainmore route. Nothing I'd classify as Dogman specifically but definitely large bipedal something in areas that shouldn't have anything that size.
The infrastructure angle is worth digging into though. Old tunnels, embankments, culverts - theres a lot of sheltered ground along these routes that most people just walk past without thinking about. Anyone mapped the sightings properly against OS maps to see if there's a genuine cluster pattern or is it just confirmation bias doing its thing?