FWIW, Amex does reverse transfers if in error, or something erroneous like that. I had an instance back when CO was a partner where I hit transfer but then got an error page, and I foolishly went back and did it again and got an error again, and then I did it again, but with the same error result. Fast forward to me checking the CO account only to see 135K points being transferred in 3 times! In hindsight I should have waited and checked the CO account first, but oh well.
Luckily I screenshotted the errors and got on the phone with MR immediately and they said they'd investigate. Shortly thereafter the points were reversed into my MR account.