As long s you use the same account your points would not be lost. For some phones it might take a while to resynch the details. The scoreboard is technically speaking Web based, so should reflect the correct Score if you restart Waze again.
I'm not aware of any major issues with the scoreboard currently.
Sent from my HTC Sensation Z710e using Tapatalk 2
Carel Cornelius AM : Centurion & Sandton, ZA CM & Coordinator, South Africa (HTC One, Android 5.0.2, v7.19.401.51)