If you are experiencing login issues with FaceID on the mobile app please see this article: Face ID Login Issue in Mobile App.
If your biometric settings, such as Touch ID and Face ID stopped working on the mobile app, you may need to disable and re-enable the setting on your device.
iOS:
To enable or disable Touch, access the device's main settings menu. On an iPhone or iPad, go to Settings > Touch ID (or Face ID) & Passcode. Then tap on 'Other Apps' and scroll down to 'Empower RET' and toggle the button off to disable, and then on again to re-enable the option for the app.
Android:
To re-enable Biometric Authentication you can go to your Profile and then 'Settings' menu. Then tap on Biometric > Biometric Authentication and tap the button off to disable and then on again to re-enable the option for the app.