The issue has been found on new Dell laptop with DW1820 combo card(BT is [0cf3:e007])
1) Use wireless hotkey to turn off WiFi/BT.
2) Wait 5 minutes.
3) Use wireless hotkey to turn on WiFi/BT.
4) Wifi is back, but BT is still off
5) Only reboot can recovery the BT state
Qualcomm releases a new firmware to fix it.
Can't evaluate it, but from our verification and S3 stress test,
there is no any issues result from the firmwares.