Your post is space on details and maybe miscategorized (see below) perhaps adding to the lack of clear post.
Are you using OneDrive? If so, see here and here and here.
Are you able to from inside the active Jupyter notebook use %cd and change the working directory to that location and use ls to list the files there?
Have you tried moving the copy of the notebook to where the other notebook worked to rule out it is permissions where your browser can and cannot access?
Aside:
You seem to have miscategorized this? Your description of using Anaconda doesn’t seem to match with ‘JupyterHub’ category.