Hello troester,
I've got the 'Fabrik Worker' problem fixed in my sandbox environment by using the GitHub link that is mentioned earlier in this thread (a different include.php in Libraries).
Than I did all the steps you mentioned above and I don't seem to have any errors related to Fabrik.
Now I will repeat all the steps again in my sandbox without using the include fix.
When all of this works fine, I'll redo this in my production environment.
Thank you for the excellent support sofar.
Q: I also discovered a folder called 'fabrik_build' can I delete that folder as well?
regards, Henk