Even if the physical device (phone, tablet, etc.) remains the same, when (re-)installing the mobile application the link between your application and your account is broken and needs to be re-established in the same way you would add a new device. To avoid mistaking devices, you should first erase the existing link before re-installing the mobile app or registering the new one.
In case you have another second factor configured, use it to access the "Manage my mobile devices" option available in My Account
From there, first delete the existing mobile device, then add the "new" one.
However, if you do not have another second factor configured with your account, or in case you lost access to it:
- Check your account type (see EU Login Help & Frequently Asked Questions)
- If you have an internal EU Institution staff account, follow the instructions from What second factor can I configure with my account? to add another second factor, then use it to log in and delete the existing mobile device
- If you have an external account, follow the instructions from An application requires a second factor authentication, but I do not have access to it anymore to remove all other factors