Really any time fifty years after the Black Death could see a Reformation-style movement take off.
The Black Death killed off anywhere between a third to a half of the poor of Germany and a bit less in Poland. This enabled the peasants in those countries, as in the rest of Europe, to gain larger tracts of land and command higher wages than they had previously. Unlike their counterparts in Western Europe though, the Central European peasants didn’t gain the same expansion of rights, and in a few cases, their rights backslid. When, two generations later, the population had bounced back to pre-plague levels, these peasants found that their wages were less than that of their parents, the prices of their crops was about the same or less due to increased production outstripping the population increase, and they now had less legal protections.
From that point on, rebellion in the HRE was a frequent occurrence that could be sparked by anything, with religious mystics condemning the hypocrisies of the Church probably being the favorites.
I highly recommend this book for more information:
https://books.google.com/books/abou...BAJ&printsec=frontcover&source=kp_read_button