Thank you for your fast answer!
I've found the issue. So i was working with the documentation here:
So as it described, I cloned the presentation to prevent changes on the source file. While doing this I could not clone any slide with a table. I've also tested this with the template you have sent me, it threw the same error.
I removed the part where I cloned the source file and just worked with the source file. Now I am able to clone all slides as it should be.
Just letting you know this. Thank you very much for the fast answer and the awesome support! Love your way to attach files, so I am able to check my files/project against yours, helps a lot and fast!