Please follow these steps:
Right-click in the middle of the screen (where the device is usually shown) and select Reload Frame.
If this does not work, try changing the device (left side of your screen).
If this does not work, try refreshing the page.
If this does not resolve your issue, try upgrading to the latest version of FlutterFlow Ctrl + R on Windows or Cmd + R on Mac. After you have done this, clear your browser cache and log in/out of FlutterFlow.
If these troubleshooting steps don't resolve your issue, please submit a bug report.