Hope to expand on this later. A community for discussing the weather (very UK), amateur meteorology, and moaning it's too hot/cold/wet/dry/mild.
A bug in the matrix or just the radar? This is no normal cloud-shape, is it?
A lot of weather radars have localized noise, I’ve noticed
The screenshot below has only one radar selected. Maybe the app you are using is displaying data from more than one radar?
Oooh, excellent point! The german weather service (DWD, which OP is using) has 17 operational weather radar... looks like an artefact to me!
EDIT: it's not an artefact, but insects!