I must admit to not being across the detail
I would have assumed there may have been a bit of Saudi quibbling as they are on the commitee and the situation in Yemen has some parralels with Ukraine. But perhaps I just have the politics of the nomination wrong in my head.
Some background to this in advance -
Saudi Arabia supports the officially recognised government of Yemen in its conflict with the Houthi Government which ousted it. As does e.g USA and UK etc.See this
for an indication of the areas controlled by each side... Marib is in the Official Government area - but close to the conflict zone. Pink = Official Gov, Green = Houthi, "Yellow" = a UAE supported group
Saudi will surely support a nomination by the official government... as long as nothing criticizes it for having damaged Marib during its bombing in support of the Official Government!!!
Russia is "friendly" with the Houthis (who are actively supported by Iran)...... but not enough to make an issue of this nomination specifically??? It would like to be a mediator in the conflict to give it an extra bit of leverage in the World!