Flickering light over southern Hesse at night. What is it?

Hello, I live in the very south of Hesse and just last night I looked up at the sky and saw flashes of light in the clouds. I'm familiar with lightning and I know what it is, but the thing is, these lights aren't very bright or synchronous. They repeat themselves several times in the exact same places over a period of a few minutes and then disappear. They came one after the other at a speed that looks almost exactly like the waves from the sonar. But you can't see them.

Unfortunately I couldn't film it.