I think that local politics play into schooling shows pretty frequently. In my area, at least half of the bigger dressage trainers are also L grads, so word gets out about how each judge likes people to ride and horses to go. And every show has judges judging 5 or 6 of their own students.
Having said that, I can only think of one instance where there was some obvious favoritism going on. But it wasn’t so much favoritism as it was the judge had to somehow save face because she was judging her next door neighbor who was flailing around on a horse with a double bridle and calling it 4th level.
I think rated shows are much less political and judges are much more neutral a.) because there are more repercussions if they are found to be not neutral and b.) they aren’t local. The last rated show I was at, all the judges were grumpy at the end of the day because they were stressed out about catching flights back home. No one knew any of the judges well enough to guess what they might like and try to change their style.
There may be examples of BNR’s changing their style to appease judges, but I assume that is because the number of active riders and judges at FEI is so small. They get to know each other like average people get to know their local dressage communities and organizations. Heck, I imagine FEI to be like your typical highly dramatic, highly political GMO.