Hi !
I just made a test on the beta with the unranked game 2976.
I obtained an unranked game numbered 3181 versus Pachiderm running at the moment Leela engine.
But when I fork the same game choosing RoyalLeela as an opponent, I get again:
“Can not play a ranked game with rank difference > 9”
I’m available to repeat the test while you look at the traces in case you’re interested 
Arnaud
Arnaud