Half of my PhD thesis is considered "unpublishable" because, after doing the work, my supervisors felt it's actually "unsurprising" that it didn't work out. We took methods that had been exploited to improve on previous results for over a decade to their logical extreme, and found that this method no longer leads to improvements. After doing the work it seems obvious. A paper on the subject would almost be considered…
I know one person who basically couldn't get their PhD because they couldn't reproduce another experiment and after several years of trying is pretty much certain the original results were faked in order to be publishable.