Hyperlink in markdown cell to pdf document stopped working

I have a large number of Jupyter Notebooks and in many of them I have hyperlinks to locally stored pdf documents. Today on my iMac the links stopped working. When clicking on a link, a new tab is opened with the proper address, but the page is just black. When I do this on my MacBook with exactly the same Jupyter Notebook, it works ok. Up to yesterday I had no problems. I have tried a number of things to resolve this, amongst others I normally work with Google Chrome, but I switched to Safari and had the same problem. When opening the pdf in either Chrome or Safari from Finder, it works fine. So it looks like Jupyter Notebook issue. When executing the hyperlink in the notebook, I get the following entry in the log file:
[I 21:56:01.222 NotebookApp] 302 GET /notebooks/Cookbooks/Git%20%26%20GitHub/books/Pro_Git.pdf (::1) 1.01ms

I get the same entry on MacBook where it works ok.

A screenshot of the page after trying to load the pdf is attached

Reproduce the local PDF hyperlink failure in a Jupyter Notebook on the affected iMac, comparing Chrome and Safari with the same notebook on the working MacBook. Start with the logged 302 request and the attached screenshot; the issue is resolved when locally linked PDF documents open normally from notebook cells.

Written by the indexing model from the issue text.