The good old ranking problem
There are two miss-ranking options. The one is over-ranking. A person is given a rank that is higher then what he deserves. This issue usually solves itself, the person will hit the glass ceiling and will stay in his current rank until he gets to the required level (or leave in frustration). This of course is bad for moral and order in the dojo.
The other issue is under-ranking. I have in my Dojo two outstanding Aikidoka with ten years of experience at Q level, who had to be literally forced into Shodan tests. This is just a big a problem as over-ranking. Ranks were designed to represent your level of Aikido. When a 3rd Q performs just as well as a Nidan it has a bad effect not only on the Yodansha but also on his peers at Q levels because they think "is this the level I am expected at Q3?" it causes a lack of confidence in ones abilities and expectation.
I find over-rankers to be ambitious and somewhat aggressive types whereas under-rankers to be slightly on the arrogant side.