Sometimes exams just aren't what you expect. It's not a reason to give up though. Learn what you can and fix that then give it another go. The ISSMP was a similar shock; many of the answers weren't in the official textbook, but were in the background materials cited.
If you've worked in IA for as many years as you have, you probably have the ability; it's probably just down to exam technique.
I failed the CAT two days ago and was shocked at how difficult the questions were. I actually took the old exam back in 2014, and I can definitely say that the new CAT exam was more difficult. Other than about 10 questions out of 150, I had no idea what they were asking me.
The questions are difficult. What helped me was that I reminded myself to calm down. With each question, I tried to think of a situation where the scenario applied to me. Some of the questions were so far fetched; I mentally convinced myself that those must be experimental questions, and I kept it moving. You can mentally discourage yourself if you ruminate too much about a question.
I hope that you intend to give it another shot
I passed the CAT on 28 Mar of this year in under 2 hours answering 100 questions. Just before the '18 change.
Based on my investigation I knew that ISC(2) had a huge database of questions that could be used for the exam. No amount of time or studying would ever allow me the visibility to all the permutations of questions that could be asked. I knew the exam methodology was CAT based on the published information on their website, the blogosphere and what I learned from my bootcamp instructor. My bootcamp instructor NEVER gave us one question to answer to simulate what is on the test. I'm sure part of it relates to the contract that you have to sign with ISC(2). I bet the largest part is due to the fact that he didn't want us focusing on the question, rather it was the material. I never used any test or quizzing sources. All I did was constantly review the CBK and mentally run the information through probable scenarios that could happen in real life that would require you to make a decision.
This cert is about how you apply information to situations to lower the likelihood of a negative outcome. You have to parse poorly written questions just like you would have to in the real world if someone is in a panic and is trying to relay information to you. You have to choose the best solution out of 4 really crappy options. You have to be able to perform well on IQ tests because this exam is closely related to that.
If you know the material well you will know that there are no absolutes. As an example, one question I had the word "All" appeared in three of the answer options. All is an absolute. I clicked the non-All option and moved on. I never read the question!
This exam is about thinking outside the box. If you are conditioned to think linearly, use a checklist of options to arrive at a solution this exam and this certification is not for you. You also have to approach this certification and this exam in context of what your career goals are. If you want to be the next Cloud data center guru this is not the certification for you. If you want to lead a team of highly gifted engineers and interact with management and customers to ensure consistent develop, operations and deprecation of systems securely this is your cert.