I just noticed I am unable to challenge anyone the ladder
The rule (I think) is you can challenge anyone up to 10 places higher than you on the ladder if they are not busy already. But if all are challenged then you can't challenge anyone until one in the next higher 10 becomes available!
I think the rule should be that you can challenge anyone not busy in the next higher 10 (as currently), or the next 1 higher that is not busy.
That protects the higher spots from too much lower ladder challenges and always offers at least one challenge if one is possible.
That will also tend to keep all highest spots on the ladder fully challenged.