Insider
Banned
Had the V2 was so unreliable as you say it was, Allies would more likely scrap them or hang them as a museum pieces. Had German engineers would be so bad as you say, they would be processed as standard nazi officials or hanged for involvement in forced labour. While OTL:You must have a very loose use of the word "good", considering more than half of their rockets exploded or didn't even hit their target. Not to mention having no effect on the war, coming close to the viewpoint of Hitler disarming his forces, for how bad they performed. The rocket program only added around 2-3 years to their programs. The US and USSR had far greater resources than Germany and would make greater strides in progress than the Germans would.
British did this: https://en.wikipedia.org/wiki/Operation_Backfire_(WWII)
Americans did this: https://en.wikipedia.org/wiki/V-2_sounding_rocket
(and of course there was a recruiting operation aimed at German Engineers, hence elements copied from V2 were incorporated as far as Redstone missiles)
Russians went further and actually copied the whole system http://www.astronautix.com/r/r-1.html
And here we can learn more about the derivatives: http://www.astronautix.com/v/v-2.html
While this cannot be disproved, I find it highly improbable. It wouldn't have precedent in previous history. While there were instances where net gain of some civilisation was lost to successors it never occurred without wide collapse of society. The closest instance could be destruction of Baghdad by Mongol Hordes in XIII century, where schollars were scattered and their knowledge faded to obscurity. However that few hundreds of scholars versus about a million or maybe even few millions with phd or masters in engineering in 40's Germany. It is far easier to disrupt system where you have one university in one city compared to system where you have close to hundred universities. Unless they win in some kind of mutual destruction scenario I can't see these people simply forgetting what they have learned, and suddenly stopping pursuing further discoveries.Considering that the science that would even be left would nothing but pseudo-science coming close to comic book logic, yes their science will effectively be gone.
Would Nazi regime stunt the growth of German science? Most likely. It can be proven that most innovative economies are those liberal, with free courts, and inventor friendly patent law.
Would it stop it or make the progress recede? Highly doubtful.