If I have understood the problem correctly, the shower starts and stops again immediately, right?
There seems to be a problem with the boolean variable Er Wordt Gedouched? So maybe the Yes and No output are triggered both in parallel?
Instead of all the other Flow Cards, add just 2 Timeline Notification Cards to the Yes and No output of the first Logica Flow Card and check it again.
I know that sounds crazy and not really possible, but I have also noticed strange things with self-created variables (see topic, just in German language). After I completely rebuild the flow, the problem was gone.
