The error indicates the python app that links to the gpio isn’t running. Usually this because python has got moved or broken. That doesn’t seem to be the case here. Are you running as the pi user ? Or at least the same one you used to install.
I am running as the pi user indeed. The flow used to work before on the same install. Might it be a missing package or something like that? Something that makes the script fail? If I try to execute it manually it doesn't do anything. There is also a testscript in the same folder as the script, but it doesn't seem to output anything. Hope you can point me in the right direction or have any idea what is going wrong here.