I have no idea what the exact problem you're experiencing is caused by, however fault-finding in all complex systems basically comes down to the same procedure: change one parameter, repeat the process which exhibited the symptom, see what happens. Then revert to the previous setting, change a different parameter, see what happens.
Make a few test panos without leaving your home. Change one thing at a time, see what the results turn out like. Sooner or later it should become obvious what's going on, if you are systematic. The key to all fault finding (which is how I earned a living for a long time) is reproduceability: if you can produce the fault repeatably more than once, you're well on the way to finding the answer.
FWIW there look to be big exposure variations in the shots you have been assembling. Can't remember whether anyone commented similarly, but make sure that you don't have exposure bracketing on. On the stitching, PTGui can use its own blending code, or Enblend or Smartblend (assuming you have installed them and pointed the application at them). They all behave slightly differently, but I'd say the variation in your sample shots is bigger than any blending application will accommodate successfully.
Systematic testing is what's required. It's easier to be systematic at home when under no pressure or obligation to get a result. It doesn't matter what the camera's pointing at so long as there are enough features for the stitcher to work with.
Roy