React Native have issue with border styles for <Text/> on iOS.
To fix it need <View/> wrapper for Cell, but don't forger to move onLayout={getCellOnLayoutHandler(index) to <View/>:
// BAD 👎
renderCell={({index, symbol, isFocused}) => (
<View key={index}>
<Text
onLayout={getCellOnLayoutHandler(index)}
>
{...}
</Text>
</View>
)}
// GOOD ✔️
renderCell={({index, symbol, isFocused}) => (
<View
key={index}
onLayout={getCellOnLayoutHandler(index)}
>
<Text>{...}</Text>
</View>
)}