Funny that this time this started from the right side of the political spectrum.
Good to remember that pretty much all leftist governments had to pivot toward authoritarianism 'for the greater good'.
AfD is objectively far more popular in the former east Germany. Look at a map of votes, it’s clear as day. The borders are exact. They are not a left wing party, not at all. They are a far right party.
It makes sense that the the economically struggling former communist areas would be both more drawn to extreme parties and have a distaste for the left.
They are a populist semi big tent party as well. They are not particularly coherent but there is some overlap between some of their policies and what some in the far-left might support (Euroscepticism, the Euro and such)