We spend a lot of time trying to predict the subjects that will be tested, but we never practice for the one subject that is guaranteed to be on the exam. As of recent, its not uncommon for professional responsibility to be tested as a stand alone essay and also as part of a cross-over question.
Professional responsibility essays are more difficult than they seem because, within the essay, there are multiple analyses for each mini fact pattern. Under the time pressures of the exam, its easy to do only one analysis and then move on, but the bar examiners are looking for how many you can spot. Doing one analysis will lower your score.
You have to practice taking professional responsibility essays. Not doing so is a huge mistake. How silly would it be to fail the California bar exam on a topic you know will be on the exam?