Basically the composite node breaks when you save your file, close and start up again if you have changed the amount of input. There are also a few other issues with the way composite works so I made a video explaining the problem.
Here you go: https://drive.google.com/file/d/15R5QwW ... sp=sharing
To summarize my suggestions/bug:
- Bug when you change composite layer input count and reopen you file
- Suggestion to change layer count order to top to bottom
- Suggestion to have composite node ignore empty inputs