V42 on GMAT Classic with 2 wrong

Can someone please help me understand what may have caused my score to go down to a V42 with 2 wrong at medium to high difficulty? My ESR is attached. I have no clue what caused my progression line to start trending down so much in the last quarter given I only missed a very hard question? My subscores were 39 CR, 51 RC and 51 SC. It also says I answered 36/36 questions so I don't think I left an answer choice blank at the end. I was hoping for a 750 and with a Q49, this gave me a 740.

I reached out to GMAT and got the following reply (it has not yet been 20 calendar days since the exam but the score is reportable for me so I assume they're saying the score is final):

Each GMAT exam goes through a two-step scoring process using different algorithms. The exam is scored both at the testing center and again when the results arrive at the Pearson VUE hub. The two scores are compared and if there any differences, the result is sent to our technical team for investigation. For a score to become reportable, all results must match 100%. The scores that are listed on your unofficial and the score that will be listed on the official score report once it becomes available 20 calendar days after testing is accurate and contain no errors. The unofficial scores are the scores which you saw at the testing center.