I may have heard an answer to this question from others, but I don't know if I've ever gotten a person in a Russian jurisdiction to explain this to me.
As far as I know, ROCOR and the Serbs have had communion for quite some time. Also, I think the Serbs commune New Calendarists. Wouldn't this thus mean that ROCOR started to lose grace back when they established communion with the Serbs ( I think this happened in the 80's, although I could be wrong).
Thank you.