Many thanks for such prompt action.
There’s an issue with the WordPress Link Library plugin page; it still reports that 5.9.10.4 is the most up to date version, despite info in the Changelog about the update to 5.9.11. This meant I wasn’t able to update directly from the plugin page. But I downloaded the zip file to my PC and installed it via FTP and your modifications to the Reciprocal Link checking page appeared.
Tried out the modified Reciprocal Link Checker and your new Broken Link checker and both worked for me. Success!
My WordPress dashboard, however, is still reporting that I have version 5.9.10.4 installed.
Delighted with this plugin and your prompt response, so have made a modest donation.
Did you notice my queries about the User Submission form? I added them into my previous query ( a week ago) about the Search form (which was probably a mistake on my part) but there has been no response from you. Should I log these questions in a separate thread?