Someone did something probably illegal and put a @riseup mail in as the contact info. Police looked at riseup (Not-in-Germany) and found some people (In-Germany) forwarding donation money to riseup. Police and state prosecutor somehow conclude that these donations might be relevant and seizes them (and the usual bycatch).
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Now my commentary: On the face of it this seems overblown and rather out of proportion. To me it looks like some AG was looking for an excuse to raid these left-wing organizations. It doesn't have to be that way, but I have a hard time imagining how some leftist hateblog I've never heard of before justifies such a large scale raid of (presumably) at best tangentially related entities. It's a somewhat different story of course if it turns out that the backers of the blog have actually been raided as well as part of these raids.