I use fetch in my react-native app for API calls.
This works fine in development builds, but slows down to several seconds in a release build.
The problem is not with the API; a request takes about 100~300 ms to complete (according to the ngrok inspector). This is true for both dev and release builds.
When I log the time before and after the fetch, there's a delay that I can't explain.
The simplest use case (even in a fresh react-native@0.56 app) slows down to a crawl when I do a API call in a release build.
console.log('start request');
const response = await fetch('http://...');
console.log('request completed');
The time between these logs varies between several 100ths of ms up to 6, 7 seconds (the non-async/await approach suffers the same sluggishness).
The response is always application/json, and I unpack it using the response.json() function. But even with a response such as {"test": 123}, it's still slow.
I can imagine having done something wrong during the react-native upgrade process, but what I don't understand is why this happens even in a completely boilerplate new react-native app.
All our tests indicate that iPods (6th gen) suffer this problem, not recent iPhones. Has anyone else encountered (and hopefully been able to fix) this?
