Supposedly, the white-throated rail bird has evolved flightlessness twice now. Sometime in the last 140,000 years, the flightless subspecies' island drowned and only the flying variant remained. Then the island un-flooded, and over 20,000 years, the flightless kind has evolved again on the same island, with a heavier body that suggests it converged to flightlessness by a different genetic route.

Is it possible that the species simply wasn't extinct?

https://www.sciencedaily.com/releases/2019/05/190509101916.htm