I have the same issue with the ceiling sometimes. When I add matching points I always remove the ones that PW5 put in. I have found that sometimes theirs are way off and if you don't remove them it will never stitch correctly. And if it's a ceiling issue and there are no points I can find I will just go into each around scene and double check the stitching points and add as many as I can. I find that by adding a lot of "known good" points it will stitch with little or no points on the ceiling.
Hope this makes sense.