When a website is using Cloudflare's email spam prevention feature, the Ahrefs site audit crawls an instance of "/cdn-cgi/l/email-protection" on every single page where an email is published. This is then reported as a 403 error.
The 403 error never goes away and the specific URLs cannot be ignored.
The only option is to ignore ALL instances of "Page has links to broken page" errors which creates risk.
Remediation:
1) Prevent /cdn-cgi/l/email-protection from triggering this error. Because Cloudflare adoption is so high, I suspect if you were to run a search in your database across all clients, >50% of the errors originate from this specific URL. As a quick fix, just ignore this url.
2) Ultimately, the solution is to provide users with the ability to ignore specific URLs within their entire Site Audit report. This will prevent false positives from being a constant nag which, currently, trains users to ignore the site audit results.