To launch the app try the following:
- Start Fortnite on your mobile device.
- Select Yes - Find my Account.
- Allow some time for a browser window to update.
- In The browser window sign in using your Epic account credentials.
After signing in you will be redirected back to the “Have you played Fortnite before?” screen in the Fortnite app - Select Yes - Find my Account
- As soon as the browser window opens, close it to return to the Fortnite app.
You should now be back on Fortnite, and the sign-in issue should be resolved.