When I try to load eg wcml over shap its blank, yet its extension is there, after verifying files makes no difference, and when I go to the store it tells me I already own it
How are you trying to find the WCML over Shap? Try a Quick Drive Scenario with any loco and pick two stations to drive between If you are looking for a Scenario to Drive those that come with the route are Career Scenarios You will only have Standard Scenarios if you install them yourself.
For me, it shows up in the Career Scenario menu, it shows up in Scenario Editor, but I can't select a Quick Drive on it, I _can_ select the _stock_ from it for quick drives, though. This persists after doing a verify cache as well.