Thanks for the ping and again, sorry about the situation.
Score cancelations remain very rare and most people have issues that contribute to it - e.g. someone entered the room, they touched their phone when not supposed to or they were mumbling or something else. There is usually a reason for it. However, if there was no issue at all, and your score was canceled, I think you should appeal and request more information. GMAC is not super transparent (and there is a reason not to disclose all of their ways to maintain test integrity) but they usually do eventually provide an answer. It may take time however, and drag on till late Dec. If you are applying in R2, that may be a tricky strategy. They clearly had a reason to move you to a test-center based test for some reason. They don't do that for everyone and we have 700+ scores every day here posted.
I think there are a few ways to look at it:
1. Did you get a personal high score that is potentially not repeatable? or do you just take it at a test center or is that a challenge? Is this more of a personal offense being questioned or do you have serious concerns you won't be able to score as high again? Those can be valid.
2. Most of the frustration that we have had was during the GMAT Online pandemic times when GMAC had only online format and you could not retake or take it a test center, so getting a score canceled was almost like a death sentence. You should appeal either way but find a way to move on and perhaps plan to retake at a test center because as frustrating as it is, you are at their mercy unfortunately.
That's all I can think of based on what you have shared.
-BB