often the blender code gets updated, and sometimes if a node’s code has changed during an update, then all nodes of that type show as ‘undefined’, which basically means they stop working.
It would be great if old nodes could be updated to new nodes when both have the same sockets, and if not possible a popup notification listing which nodes need manually replacing.
I’ve just done a 3 hour render, and my options are to start re-wiring a massively complex node tree which is driven by drivers, or re-render.
If the file output node had a save button, then that would help. hmmmm or perhaps it has an un-exposed save function via python. I’ll investigate.