Unfortunately, there are more DOIs that resolve to broken links than we would like. This is because the URL that the DOI link goes to needs to be updated by the publisher when that URL changes -- and not all publishers are very good at updating their Crossref records.

If you have URL Checking, note that this module always skips DOIs because the DOI URL will always resolve to a different URL. Since redirection is something URL Checking looks for, it would insert a lot of false positives.

The best thing to do when you encounter a broken DOI is to report the issue to the publisher and keep the DOI in the manuscript. The DOI is correct, even if the link it points to is broken. A broken DOI link will hopefully help remind the publisher to update their records. Of course, it is up to you whether you keep the DOI in the manuscript or not.