A review of the plant’s page on Wikipedia shows that it did indeed have a number of low level incidents. Do you have any sources about those being the true cause of the shutdown?
I don't, and I'm not sure it's possible to figure out exactly — since it's politically sensitive and possibly involved "back channel pressure" and other shenanigans.
That said, it has been a longstanding topic in German anti-nuclear circles, cf. list of articles (German) on: