Why does `react-native run-ios` show "No bundle URL present" until I reset it?

With my React Native app, when I run react-native run-ios, it shows this screen:

When I press cmd-R to reload, it goes away. This happens most, but not all of the time. It's not just with a particular project; when I create a new project from scratch, it's the same.

I'm sure this could happen for a variety of reasons, and I'd need to give more info to narrow it down, but does anyone know how I could approach figuring out why this happens?

It happens because your simulator opening the app faster than metro bundler server. In my case, it's often happened when I stop the metro bundler server and still have simulator running my applications and there is a warning message that saying metro bundler is not connected. Either way, as long as reloading the app still working, that means there is nothing wrong with your react-native configuration.