I have to admit that this is not my area of expertise and your question is pretty specific but I did a google search of "ultrahigh energy cosmic rays" and found some good stuff out there.

So it seems that people aren't really sure where ultrahigh energy cosmic rays come from or if mergers of galaxy clusters or galaxies are a source of ultrahigh energy cosmic rays or what mechanism in a merger would accelerate the cosmic rays. So, I think it is safe to answer your question with "no one knows for sure" but I imagine that the scientists who are doing active research in the field have varying opinions.