Man, this is like watching a thumbnail that looks fine but gets zero CTR-it's a crawl issue, not a campaign one. I've been burned by this exact thing. A URL works perfectly in a browser but Google's crawler gets blocked by something dumb: a firewall rule, a plugin update, or a redirect chain that loops back on itself. The trick is to stop treating the URL like a viewer and start treating it like a bot.
First thing I'd do-check Search Console's URL Inspection tool for the final landing page. See if Googlebot can actually fetch and render it without errors. If it shows a redirect loop or a blocked resource, you've found the drop-off point. Then dig into what changed recently: maybe a security plugin, CDN setting, or robots.txt tweak that treats the AdsBot differently from a normal user.
Honestly, half the time it's some cache or firewall rule that got flipped during a site update. I wouldn't touch the campaign settings until I've confirmed the crawler can even reach the page. You're basically doing a retention chart analysis for the crawl path-find where the drop happens, fix that, and the eligibility should come back.
