Electrics: Windscreen wiper stops at engine start

Hello, maybe someone can help me.

Flashers & windscreen wipers often do not work - if you start the engine.
As long as the key in the ignition lock is turned to the position before starting the Mtor (position 2?) everything works.
If you then continue to turn and start the engine, both turn signals and windscreen wipers are without function.
Bzw the wiper stays on the disc where it was when the engine started.
You can then try again with the engine start and after some attempts go turn signals and wiper- despite running engine again.

Extremely annoying.
I want to make the mistake.
Does anyone have any idea what it might be about?

Thank you for your answers,
Jörg