This is almost certainly a bug since 3D Touch continues to work, it’s just that there’s no feedback from the phone indicating that 3D Touch was used. Users reported this issue through iOS 10.2, but there are a few things to try.
Restarting the phone will temporarily restore haptic feedback.
1, Go to Settings > Sounds & Haptics and toggle System Haptics off and on again.
2, Go to Settings > General > Accessibility > 3D Touch to toggle the feature on and off, and to adjust the sensitivity.
3, If you have Skype installed, some have managed to restore feedback after disabling the app’s integration option.