Now, are you finding the same things in your own parts of the country and does anyone know what they are?
The problem with uncurated route sharing sites like OS, there are no quality controls on what people can and do upload. If some one plots a route that takes you straight over an 80m cliff such as Malham Cove or Cheddar Gorge, the website will show that route, however implausible or suicidal.
The routes in OS you have highlighted such as "191-012" are simply two waypoints connected by a straight line. Presumably someone (possibly a 4x4 off-roader?) was doing some route planning which involved flagging likely sections of PROWs to link up and made these Public rather than Private. Not only that, they managed to upload them multiple times!
While there are plenty of uploaded routes containing unedited multipath and masking errors, spurs and point clouds, I haven't come across these two-waypoint routes in my areas of interest on the OS site. However any uncurated GPX routes you download from any site should be treated with caution and carefully checked, just as if someone you don't know drew a line on a map and told you to follow it!