As a judge myself, I can honestly tell you: The whole trouble with competitions is that they are judged by humans. And as such, there can be any number of things to screw up a human's judgment.
1) They might not be trained or certified in the BJCP program.
2) They might have eaten onions or garlic the night before, or just smoked a cigarette, or didn't bother to brush their teeth.
3) They might have a head cold.
4) Their palates might be fatigued from already having consumed dozens of beer samples.
5) Their mom/spouse/children might not love them.
6) They might have a really weak personality and believe that if the National judge sitting next to them detects the slightest hint of DMS or diacetyl, then by golly he must be right and it's a terrible beer, even if they don't detect the same thing.
7) They might have time pressure to get that scoresheet out in less than 5 minutes.
It is for these reasons that I always recommend that if you want really good feedback from competitions, you NEED to enter each beer in not just one, not even just two, but THREE competitions. Then you'll have at least 6-8 scoresheets, and can look at all of them at one time, and throw away the ones where the judges obviously did something stupid or didn't know what the hell they were talking about. After throwing out half of the scoresheets, you're left with maybe ~3 good scoresheets and can make improvements in the future based off those.
Seriously, this is exactly the process I've used to get the most out of competitions, and I think I'm making better beers because of it.