looks a bit like convective cells to me! they happen in summer (as long as there is sufficient surface heating to drive the convection) - they're like bubbles in boiling water.
It looks like you've got high pressure over there though... the high pressure may just limit the cloud heights and intensity of the precipitation?
Edit: these look a little too big to be pop-up cells, but they still look more convective (instead of frontal). a bit suspiciously too round, though.
Do they stay consistent and track across the sky, or are they more bubble-like?
2nd edit: looks like I'm wrong and it is a radar artefact :) (this is why looking at radar timelapses is more important than just single-frames!)
3rd edit: it's not an artefact, it's a real signal! it's insects!
aha here's a full explanation of the thought process:
no other weather report matches these patterns
they're suspiciously round and not blobby like real clouds
they're each suspiciously localised around the radars in the network
there are lots of types of radar artefacts, including close-to-radar ground-clutter (this is what I assumed it was) but it's too consistent and large of a signal for that
so it must be something uniform, in the air instead of on the ground, that isn't rain
bugs are about the size of a big rain drop! enough to be picked up as a strong signal by the radar and enough to prevent the radar from seeing long distances
It's also been flying-ant-day recently across Europe
Doesn't look like orographic cloud to me! Usually they have ripples in em
Plus, the Alps are only really in the South and nowhere near Berlin (which is pretty flat) - so you'd see more enhancement in the South than the North, whereas these are pretty evenly spaced