Oh wow—I had spent hours working on this today, but as soon as I typed that, the next thing I tried finally fixed it.
The problem was that in my api\src\services\scraper.ts I had written import { getWaitTimesResponseGAGwinnett } from 'src/lib/scrapers/GA/Gwinnett.ts'; instead of import { getWaitTimesResponseGAGwinnett } from 'src/lib/scrapers/GA/Gwinnett';.
Removing the “.ts” from the import lines fixed the Netlify production build. 