heyyy the STL check fixed it O_O i never use that thing, do u just need to apply it and it fix the problems for you? cause all did is applying it and it was ok (i though it only points you out the errors?)
Sure you don't have double edges ? Really looks like it to me. The points could be welded but not the edges, it happens sometimes. Select the edges and make a weld ? Also, yeah the STL check is a pretty useful modifier for checking bad topo.