It seems to me the update mechanism is bricked somehow.
I just tried to update one of my test systems from v2.575 to v2.587. No system files have been modified, but i get this:
Update-bricked.jpg (139.02 KiB) Viewed 145 times
I also noticed on other of my systems - for a while - there has been offered v2.588 and v2.589 beta versions. Short time later the beta versions haven't been offered any longer and these 2 systems now also are stating i'm on the latest version. Didn't think too much about it because of beta status - but now i'm trying to update a clean v2.575 system to v2.587....
I will have a look to find another older system and retry.