Disappearing URLs in Core Web Vitals on Google Search Console

Since the recent updates to Google this summer, the number of "Good URLs" reported in the Desktop report of the Core Web Vitals area of Google Search Console has gone from 300+ to 12. They haven't simply been relabeled as Needs Improvement or Poor either, they just disappeared.

There's plenty of information about how to improve URLs that are Poor or Needs Improvement, but I can't find any explanation about why URLs would disappear from the report all together, or how to fix that.

Can anyone help me understand what's going on here? And what action I should take if any?