Failed to load resource: the server responded with a status of 404 (Not Found) screen:1

Ionic Framework ionic-v3
1

Hi, i’m working in a Ionic 3 application, running with “ionic cordova run browser -lc” cmd my application starts correctly but from the Chrome console I see these errors:
Failed to load resource: the server responded with a status of 404 (Not Found) screen:1
Unhandled Promise rejection: Missing Command Error ; Zone: ; Task: Promise.then ; Value: Missing Command Error undefined
n.onUnhandledError @ polyfills.js:3
ionic3-err-screen

How can I look for the origin of these errors?
Thanks for help