This will try to join every element to every other element (regardless of whether or not they’re even touching) and create a huge list of new, combined elements.
You’ll have to iterate through your lists if you want to end up with a single element on the other side, e.g. something like take one element, then check for intersections with the others, join those, and repeat for the remaining elements…
See also this post of someone else trying to do the same Elements Joining