Not for the first time recently with Node-Red (Raspberry Pi 3) - even using Dave's node/nr update script, and despite having a working setup before then doing updates in the palette manager, I find myself having to resort to a backup as NR says it can't find i2c-bus and stops. I then restart NR and it now says it can't find a boatload of other nodes. The backup before using palette manager to do updates is fine.
Do you have the actual log message to share? Doesn't give us much to look at otherwise.
Is the update script you are using the on at this page:
I have had some similar issues that indicate to me that there are some hold-over 'ghosts' from a previous version or install. A clean uninstall/install fixed it.
Solved issues, NR and LOTS more now installed, running, backed up and replicated on Pi2 and Pi3. Thanks to all for comments and help.