An Android emulator comes with the Google Android Studio. The emulator includes a pre-installed browser, which is surprisingly not the Chrome for Android.
That browser gives an error “The certificate isn’t from a trusted authority.” for the certs signed by the Let’s Encrypt. But the same browser can access other https sites without any problems. For example, it can access this very forum https://community.letsencrypt.org.
Is that an emulator problem? Or, can Let’s Encrypt do something about it?