Great that you're focusing on reviewing your FLs in great detail. This is how I saw the most improvement in my score (517 - 126/129/132/130). I've attached a couple of screenshots from a spreadsheet template I used in reviewing all 10 of my FLs. This is from a very early one Kaplan FL2 (spoiler alert - only a few explanations per B/B and CARS sections).
I really would try to tease out why you missed the question. Sure, it really could be content, but as you can see in my descriptions, I only considered wrong answers content if I thought a flashcard with a definition would have seriously allowed me to pick the right answer. A lot of the time, I found missed questions to stem from a misinterpretation of the passage, q-stem, or lack of comprehension of the passage itself. I would then assign homework that either entailed content review from another source I haven't already tapped into; or if it was a test-structure issue, would initially go back and outline that entire passage with question headers on a sheet of paper asking the following types of questions: What is the main purpose? What bits of information do I need to know? What is the q-stem getting at? How can I explain the other answer choices as wrong? Finish the entire review guide + homework assignments first, then go back and do the homework assignments.
I found after doing the outlining for several passages later, I started to have - by far - less error due to misinterpretation of passage/q-stem. Continue to adapt as you improve. You may not have to always assign homework if it was just a silly mistake or if you can simply make a content flashcard and move on. Lastly, make flashcards. If it is a simple concept you didn't know - make a flashcard. Formula? Flashcard. P/S theory? Flashcard. Make it and move on. Don't waste too much time overkilling a content area that you will see again, guaranteed.
Feel free to DM if you have any further questions. Good luck.
