Mobile keyboard interferes with full screen modal in react native app

I have a spinning loading wheel (implemented with <ActivityIndicator>) inside a modal with lowered opacity. I want the modal to cover the full screen. The modal pops up after the user unlocks their account in another modal. The problem is that the ‘loading wheel’ modal only covers the part of the screen that wasn’t covered by the keyboard in the ‘unlock’ modal.

It would seem to be a timing issue as occasionally the ‘loading wheel’ modal does cover the whole screen. Here’s my react native modals:

<Modal visible={modalUnlockVisible} animationType={"none"}>
     <Text>Enter Pin Code</Text>
     <TextInput 
          maxLength={15}
          secureTextEntry={true} 
          onChangeText={text => setPincode(text)}
      />
      <Button 
          title="Unlock"
          onPress={() => { Keyboard.dismiss(); unlock(pincode) }}
       />
</Modal>
<Modal visible={loader} transparent={true} animationType={"none"} style={styles.loader}>
    <View style={styles.loaderBackground}>
        <View style={styles.loaderFrame}>
             <ActivityIndicator size="large" color="#006EFF"/>
        </View>
    </View>
</Modal>
......
//styles
loader: {
    zIndex: 100
},

loaderBackground: {
    top: 0,
    left: 0,
    bottom: 0,
    right: 0,
    flex: 1,
    alignItems: 'center',
    flexDirection: 'column',
    backgroundColor: 'rgba(0,0,0,0.7)'
},
.....

So the top modal of the above two pops up, and the user unlocks by pressing the Unlock button calling unlock(pincode):

function unlock(pincode) {
    setModalUnlockVisibility(false);  // Hide 'unlock' modal
    setLoader(true);  // Show 'loading wheel' modal
    .....
}

Any way to make the ‘loading’ modal cover the whole screen? I added in the Keyboard.dismiss() before unlock(..) in the hope that it might help, but the problem persists most of the time.

loaderBackground: {
    width: Dimensions.get("window").width,
    height: Dimensions.get("window").height,
    alignItems: 'center',
    flexDirection: 'column',
    backgroundColor: 'rgba(0,0,0,0.7)',
    ....
},