Starting 2019-08-01, Google will require all published app updates to provide 64-bit versions of any native code.
https://android-developers.googleblog.com/2019/01/get-your-apps-ready-for-64-bit.html
https://developer.android.com/distribute/best-practices/develop/64-bit

We don't currently meet this, due entirely to a number of libraries built into React Native.

Google originally announced this requirement (and deadline) with nearly two years of lead time, in 2017:
https://android-developers.googleblog.com/2017/12/improving-app-security-and-performance.html
and there's an issue open for it upstream:
facebook/react-native#2814

It's said to be fixed in master, so when we upgrade to v0.59 that will hopefully take care of it.