What can make a functionality run a simulator and not on the device? - react-native

Question

I'm building an app using React Native.
I'm fetching an array of values fetched from a database in order to provide users a line chart which refresh every X seconds ( 3s atm ).
This works fine on iOS simulator but when it comes to deploy to TestFlight, and run the app on a device, the curves are not displayed, nothing happens.
Since I can use some other feature that requires to fetch data from the DB, I figured out that the issue was not from the API requests.
I currently use react-native-chart-kit, but I tried with react-native-svg-charts as well, the issue remains the same.
Any hint ?
The issue is the same when I display the array of the fetched values, a new value appears on the simulator every 3 seconds but it does not show anything on the device.

Answer 1

I finally found the issue.
The issue were spotted at the API request.
My request takes 2 timestamp params : start time / end time
I always debug the app using the browser and launch ios sim from the RN project.
This time I tried to Run a the project from Xcode and edit the Scheme as release instead of debug .
When I checked the console from Xcode I noticed that my Start time timestamp when considered as 'NaN'.. Not the End time timestamp.
Back to the RN project and to the browser console, the timestamp is alright.
I made some random changes and now it works fine .
Here's what I had before solving the issue:
function formatDate(rawStamp) {
const now = new Date(rawStamp);
var convertToStr =
now.getFullYear() +
"-" +
("00" + (now.getMonth() + 1)).slice(-2) +
"-" +
("00" + now.getDate()).slice(-2) +
" " +
("00" + now.getHours()).slice(-2) +
":" +
("00" + now.getMinutes()).slice(-2) +
":" +
("00" + now.getSeconds()).slice(-2);
return convertToStr
}
const nowStr = formatDate(Date.now() - 7200000)
const gameStampMinusX = Date.parse(nowStr) - (300000)
const gameStampMinusXToStr = formatDate(gameStampMinusX)
Here's what solved the issue:
const nowStr = formatDate(Date.now() - 7200000)
const gameStampMinusX = Date.now() - 7200000 - 300000
const gameStampMinusXToStr = formatDate(gameStampMinusX)
I'm a newbie so I cannot explain this behavior, but seems that this little change makes Xcode recognize the timestamp, and proceed the the API request correctly.
If anyone can explain, feel free !