That's what I meant, Allira. Mandelson has been associated with all sorts of sleaze, but somehow has managed to squirm his way out of serious consequences. I know no more than anybody else and if something else is revealed, it could prove I'm completely wrong. However, I'm basing my judgment on what is known for a fact. Mandelson certainly knew Epstein, but as far as I know there is no suggestion that he was involved in anything illegal. It's possible that the vetting picked up on one of the reasons Mandelson was sacked previously. If that's the case, Robbins might have decided that the public already knew about his previous dodgy dealing and, therefore, he wasn't a blackmail risk.
Goodness knows what prompted Starmer to want him as ambassador in the first place. If my memory serves me correctly, Trump wanted Farage. It would be interesting to know whether he would have passed security vetting. I think people are correct when they claim that Trump's election has meant that all "normal" rules have been thrown out of the window. Starmer possibly thought (or was advised) that Mandelson would be able to beat Trump at his own game.