Perhaps try holding the power key for longer than 20 seconds to initialize a software reset.
When the phone resets check to see if the front camera starts.
i had this issue, waited for updates reset phone manually and through WDRT, left insider ring, tried everything, eventually got a replacement
sorry to say i think its a hardware fault.
i'm on 1607.576 and have the same thing with front camera, soft reset doesn't works, and if some app is taking front photo (also after restet ) freezes too.
My wife's and sister's 950XL doesn't have this bug..