It's unlikely that you've actually gotten worse in SC, unless you somehow studied grammar rules that were completely wrong! My hypothesis is that one of two things is happening:

1. You're getting harder SC questions. Remember that the test is adaptive, so improvement in any area makes all of the questions you see harder. Your CR went up significantly since CAT 1, so imagine this: perhaps you got a medium CR, got it right, and the next question was a hard SC. You got it wrong, so the next one was a medium CR. You got it right, then got a harder SC. It's possible that this accounts for some of the difference.

2. Timing. Often when students improve their content knowledge, it's at the expense of good timing balance. If you had a chunk of SC at the end but didn't have time to solve them, this would drag down your SC score.

Regardless, I think it's fair to say that you should put in some work studying SC. I would pick up another strategy guide to see if a different set of tactics resonates more. Make sure you study the rules and also put them into practice by doing sets of OG problems. If the practice tests are the only official questions you see, you're not doing enough real problems.

Here are some of the most important things to know to improve SC:
https://www.manhattanprep.com/gmat/blog ... orrection/
https://www.manhattanprep.com/gmat/blog ... ap-part-1/
https://www.manhattanprep.com/gmat/blog ... d-writing/
https://www.manhattanprep.com/gmat/blog ... n-problem/
https://www.manhattanprep.com/gmat/blog ... -tell-you/
https://www.manhattanprep.com/gmat/blog ... ce-part-1/
https://www.manhattanprep.com/gmat/blog ... o-i-start/

You should also carefully track your mistakes in SC. Here's some advice on how to make an SC Error Log: https://www.beatthegmat.com/best-practic ... tml#763957