RStudio fails to save changes to Rmd in cases where the notebook has duplicate labels.
Although the top of the file shows an error as "Error creating notebook: duplicate label 'this label'." it does not make clear that a save failed to happen and the * indicator will go away (as if it did save).
I've lost changes as a result of this. I don't generally care if the html associated with a notebook is generated and don't see why I need unique labels.
As it so happens you do need unique labels (for example, in the notebook you've screenshotted above, the plots generated from those two chunks would overwrite each other because they are named by chunk labels). So, at the very least, a temporary fix would be to use them.
This bit I don't know the answer to – just pointing that out for disambiguation purposes.