It's being triggered by a fear of mass immigration and the fear of potential dire effects. Much of it is being whipped up with dog whistle politics. East Germany doesn't have high immigration. It's had billions of post-unification investment and huge opportunities have been created, but they're unfamiliar and new opportunities. And with East Germany you have a population demographic that reflects that anyone with education and aspiration (mostly young women) moved West in the decade after the wall came down. The remaining population has a consequential education and gender imbalance that is slow to resolve.
What we're seeing in the rise of the right-wing is a backlash against post-industrialisation that's finding a scapegoat in immigration and 'foreign'. Communities that have over-invested their identity in heavy industry (coal, steelmaking, etc.) are losing that identity with post-industrialisation. Their fears are are being stoked to form new community identities under a banner of Down With This Sort of Thing. They're being exploited by grifters filling the identity vacuum with fear.
You can see the dog whistle most clearly with someone like Farage, who's constantly aligning himself with marginalised communities (he's done it with fishing, he's now doing it with Clacton), he expresses concern, shouts about unfairness, gets himself into a position where he could make positive change, and then does fuck all because he's earned his grift and can live on that for a while. Rinse and repeat with another 'concern'.