Ok this is almost working, I added your code into the Snipptes and it detects the listing but is not able to update the list. Sometimes it breaks the whole browser, be careful if you want to check https://kjfs-lyss.ch/wordpress/
Anyway, I have absolutely no idea what to do but to tell the client it is not working anymore, deal with it and with a litle hope it will work again sometime in the future 🙂
Thank you anyway for your help! Very nice and helpful support (eventhough my issue wasn’t fixed 😀 )