@mararm As I said, those users on different instances are actually one user (e.g. you at loadaverage). They are copies of the same user. This User is local for loadaverage dot org and remote for all others.
Using local user IDs in server-to-client interactions instead of global WebfingerIds is a cause of such "multiplicity problem" and is current limitation of both GNU Social and, sadly, of #Mastodon also. More details - in this post and below: https://github.com/andstatus/andstatus/issues/419#issuecomment-254028055