Thanks for all this. I was experimenting with RFC IDs to see if it affected a very strange problem I am having.
I am trying to sync some GameObjects but when connected to a server their Y position is off by about -745,000 units! This is happening on the host when connected to a standalone server and is extremely hard to nail down as it is not always present.
If I comment out part of my SetPos RFC (the transform.position =

part) which is not even executed on the host the problem goes away. If I uncomment it again the problem will stay gone away until randomly returning and staying. Even after rebooting (C&S concurrently) and clearing everything it is still present. Very annoying and time consuming! I have been doing Unity for 4 months, after more than 20 years of C++ app and game coding nothing prepared me for how fiddly Unity can be sometimes! I found UE4 C++ a lot easier.
I would love to post about this much bigger problem but I can't pin it down and am not even sure it is directly related to TNet as here is lots more going on.
Anyway I am working away on trying to work this out. The RFC numbering did not affect this problem but this is how I got here early on.