Viewing elevation changes the route

Strange behaviour on this route: https://cycle.travel/map/journey/182694

When I first open the route, it skirts west of Banbury:

But then if I open the elevation pane, my route changes. It now goes through Banbury. 

How is the maximum gradient calculated?

Here's an example screenshot. The maximum gradient is showing as 3.4%, whereas the local gradient under my cursor is showing as 8.1%.

Where does the 3.4% figure come from?

Waypoint won't snap to footpath

Sometimes waypoints will refuse to snap to certain footpaths.

E.g. https://cycle.travel/map/journey/147632

Between waypoints 9 and 10, there are a couple of footpaths. I can't get the waypoints to snap there, and I can't get the route to follow the paths. 

I do realise footpaths are dodgy ground for cycling. But generally it is still possible to force cycle.travel to route along footpaths. I'm just wondering why I can't route along these specific footpaths.