An ads.txt file can be reachable and still not explain the warning

A site setup note about exact-domain ads.txt checks, publisher ID lines, redirects, cache, and reprocessing time.

Seeing ads.txt in the browser is only one check. I would still verify the exact domain version, publisher ID line, redirects, cache, and the time the corrected file became reachable. The warning may need reprocessing before it disappears.