Html pages in content not generated to public after upgrade hugo from 0.25.1 to 0.37


We used to use 0.25.1 to generate multi lan version of a website, the source structure is shown below:

After we run the hugo command, localized pages will be generated to public/en-us and public/zh-cn respectively.

But after we upgraded to 0.37, only the index.html is generated in public folder, all others pages seem to be ignored. Is there configuration or layout change between 0.25.1 and 0.37 that may cause this? How should we fix it?

See here and here and here

Also read about Page Bundles.