It could be caused by wrong Cardboard viewer settings. They are used to setup the cameras, the projection matrix and the distortion mesh. On Android they’re globally cached and restoring the default values is hard. But you could simply scan the QR code for the original V1 (or V2) Cardboard and check if it fixes the problem. You can find such QR codes here https://homido.com/en/les-principaux-qr-codes-pour-casques-vr-passifs/.
If still developing for Google Cardboard, you could also be interested in our plugin “Cardboard VR”, that integrates the new Google Cardboard SDK in UE4, for both iOS and Android: https://www.unrealengine.com/marketplace/cardboard-vr .