Sounds like you might be mixing up the two boundaries? It can get a bit confusing. The minimum ranking is the minimal strength of your opponent which in kyus is the BIGGER number. The settings do not allow inputs the other way around as it would made no sense and hence default to the closest possible settings which is one rank for both.
In a way it might also explain your other problem too. If that is not the case sharing a screenshot of your settings might help us look further.
I created a game restricted to 10-1kyu (“min: 10kyu, max: 1kyu”) and it was accepted by a 11.9 ± 4.9 kyu player (i.e. a new account).
Is this a bug or am I misunderstanding how “restrict rank” works?