FWIW I just updated to 6.5 because it seems to address the issues I had previously, and I’m not having the issue with the RC number being reset. Sorry you’re experiencing this; it’s understandably frustrating. Have you looked into the KMLink Plugin? It’s a great plugin that every KM/SD user should have.
For more info on the difference between the native KM plugin and the KMLink plugin, see the tutorial I wrote about it a couple of years ago (link below).