Could you provide links of a few URLs for these links? Also, to be sure, which type of check did you run on the Link Checking tool page?
I cannot provide access to the inside links, but here are a few of the external links it reports as 403 or unreachable, and screen shots of inside stuff it also claims it cannot reach.
I was using this tool: https://i.imgur.com/FezUUxF.png with no options checked.
From the server, or my pc direct, I can reach these locations.
Reports Unreachable
ANPI Online https://www.anpi-online.org
Auglaize Co Auditors https://auglaizeoh-auditor.ddti.net/
Chase Paymentech https://secure.paymentech.com/signin/pages/login.faces
Reports 403 (internal links)
APMax Portal https://apmax.telserco.com/Notify/ (https://i.imgur.com/nJ3WjWc.png)
Adit 600 https://one.telserco.com/docs/support/adit-600-channel-banks/ (https://i.imgur.com/0TsbvDy.png)
Indeed, there was a flaw in the broken link checker logic with recent changes that I made to the plugin. This will be corrected in version 7.1.1 which I’ll release later this evening. Now, the ANPI online link that you provided still won’t check properly since there is a login dialog that appears as soon as you visit the site and that throws off my link checking code, but I expect other regular pages to stop being displayed with error codes.
Please let me know if this resolves the issue and consider donating to support this plugin’s development.