Need HELP to Improve Sentence Correction!

Hi everyone,

I am kind of desperate and looking for a solution to improve my GMAT score. Thanks in advance for reading and suggesting ways.

First of all, a little background about me; I am a non-native English speaker, but living abroad and using English all the time in daily life. I started to prepare GMAT 32 days before the real exam. I did five mocks (GMATPreps and Manhattan) in this period. In all of these mocks and also in the real exam my Quant was 51 straight - so no problem there and I didn't spend any time for it. Also, IR was 8, another time-saver for me.

However, it is the opposite for Verbal, especially for SC. In 32 days, I spend around 75 hours and at least 60 hours on SC. I studied from MGMAT and e-Gmat, I solved all questions on OG and Verbal Review, I took notes, I created an error-log, I used GmatClub a lot to understand my mistakes, and so on. The problem is my accuracy on the practices is around 80-85%; however, somehow in the real exams, it can go as low as 30%. For instance, in some mocks, I got 730-700, but in some of them I got 640, and all this difference is mainly coming from SC. If I 'guess' correct or if I am 'lucky' about the questions, I can score high, but otherwise, the result is unsatisfactory. Consequently, I resulted in 660 in the real exam and still no clue how can I consistently increase my SC score. I mention SC because my RC or CR mistakes are 2-3 max. in each exam, whereas SC can go up to 8-9.

I think my main problem is that I am unable to understand what is the issue in the sentence. I understand the sentence, if it is an obvious mistake, I can fix it, but otherwise, I struggle a lot. I think my accuracy when practicing was high because when I practice I knew what the question about was. Also, in theory, I know almost every 'rule' (i.e. like vs as, modifier, pronouns and so on) but I feel especially in the new 2020 questions and exams the sentences are somehow different -more direct- so if you are not really good it is hard to understand what is the problem. It can be because of the fact that my grammar foundation is not so strong as a native, I am not sure.

All in all, I really need some advice about what to do. I decided to give myself around 10 days rest before preparing again. I am planning to study for another 75 hours in 30 days before the second attempt. I just don't know what else should I do or where else should I study from?
Should I re-do Manhattan and e-Gmat again? Or try something else? I don't I need a tutor, but is it a must since my initial method didn't work?

Thanks a lot in advance. Oh, btw, my target is 700+