When writing fader automation in very large files I was getting horrible freezing / jumping / stepping (call it what you will) of the timecode and timeline and the automation was updating every second or so, so it was unusable. The system would play back and read automation perfectly and this would only occur in automation write.
I found that the problem was being caused by having the Overview Line turned on in the very large project. Once I turned it off the system ran like a dream. This never used to be a problem in N6.