As Squishy said, decompiles are imperfect, and usually cause optimization brushes such as areaportals to become slightly misaligned, causing your compile to fail. BSPSource automatically makes a visgroup with optimization brushes that require your attention, so take a look at it in the user visgroups window.
There is no "perfect" Upward VMF available as Valve has not released one. The only VMFs for Valve TF2 maps out there are the ones that came with the Source SDK ten billion years ago. You can find those
here, just be aware that most of them are outdated now, as bug fixes have hit some of them.