After the latest SnapBridge update, Nikon released the corresponding firmware updates only for the D3400 and D5600 cameras but not for the D500. The D500 firmware update should be released at the end of March according to this email response from Nikon tech support email (the latest version of Snapbridge is reportedly not working with the D500 and iOS 10.2.1):
Yes, a new firmware update for the D500 is in the works and should be released by the end of March to address the connection issues users were having with iOS versions 10 and above. We have the new, updated version of Snapbridge to address the issue as well.