Why is my jupyter notebook .ipynb file NOT updating when I download it as a .py file despite making changes in the .ipynb file?

Question

I have just encountered some very strange behaviour in Jupyter Notebook. I edited an .ipynb file and downloaded it as the .py file equivalent. However, when I look at the .py file, the changes have not been made. It is as if the download as function is referencing an earlier version of the .ipynb file somewhere, but I cannot understand the behaviour.

I have tried renaming the .ipynb file and then downloading it again and it DOES update in the new .py file. Then I change the file name back to the original .ipynb file name and save it again as a .py file BUT it reverts to the original unchanged .py file.

Any ideas or explanation here for what is going on and how to fix please? Thanks!