It doesn't look like Assad is going anywhere, so what is the problem engaging in some diplomacy? If they were arming him, then we would have something to talk about. Let them take care of their own regional politics without some smartarse football journalist sending emoji tweets.
Look, we can't get away from the fact that Mansour is part of the royal family and involved in some capacity as a government representative. It only matters in two situations: i) he owns us as a proxy for the state. He doesn't and, imho, that will never be challenged where it actually matters, or ii) the UAE detaches itself from a policy of what we call modernisation, and starts working against western foreign policy and then he becomes the UAE's Abramovich to the UAE's Putin. That won't happen, either.
I would relax a little.