In a different thread you wrote that "as you say, the MWI claims that in each branch of the wave function, the human experiences a single result of a measurement." But here you're saying that MWI makes a claim that contradicts that we observe measurements to have single results. MWI, just like Copenhagen, claims that we will observe measurements to have single results (but that we won't be able to predict in advance which result we will experience observing). MWI's predictions are exactly in alignment with what we observe, and makes no claim that in any way differs from the reality that we experience. If it did, then it would be falsifiable.
I agree. Others (not you) elsewhere in this discussion have said otherwise.
> here you're saying that MWI makes a claim that contradicts that we observe measurements to have single results.
Yes, overall I think the MWI contradicts itself in this regard. It has to say that measurements have all possible results, because that's what Schrodinger's equation says, but it also has to say that we observe measurements to have single results, because it's clear that that's what we actually observe. I don't think its claimed resolution of that contradiction is valid. But you are correct that that is not an issue that can be resolved by experimental tests.
Yes. All of those questions are open areas of research in the foundations of QM. There are no generally accepted answers to them, although of course each individual QM interpretation has its own set of preferred answers, and physicists who prefer a particular interpretation will often talk as though their preferred answers are generally accepted--but they're not.
> which MWI claim contradicts observation?
The fact that we observe measurements to have single results. The MWI claims that every measurement has all possible results, but that this fact is in principle unobservable. That makes the MWI unfalsifiable.