You cant export your private keys, i tried doing by going to developer option and then assets and then bitcoin, but all i can export is bitcoin address... even if you click export private key or address the output is same, only address is exported.
This is a bug from 1.27, It should be fixed on the next update (this Thursday). You still can downgrade to 1.26 and export your private keys in the meantime If you want to otherwise just wait for the next in a couple of days.