React native ActivityIndicator keeps animating even after it is unmounted

Question

I have some code which displays an Activity Indicator for sometime, and then renders an expensive Component.

Here is the code for it

class MyComponent extends React.Component{
  constructor(){
   this.state={isLoading:true,...someOtherStateProps}
  }

  componentDidMount(){
    InteractionManager.runAfterInteractions(()=>{
     /* Expensive Calculations*/
     this.setState(ps=>({isLoading:false}))
    })
  }
  render(){
   if(this.state.isLoading)
     return <ActivityIndicator/>
   return <ComponentThatRendersALongListOfItems/>
  }
}

My Problem with this code is, if there is an ActivityIndicator present it takes a hell lot of time to actually render the Main View even after I set state of isLoading to false. If I replace that Activity Indicator with a return value of null or Loading..., I see my main Component with a very short delay. I placed 2 console logs in the render method to confirm if the return value was from the if part or the main part. I think even after ActivityIndicator is unmounted it still keeps animating which blocks the main thread from rendering the Main component. Any help or advice?