OK It is now Wed 20 Feb 2019 and I have been fighting this stupid problem with my D7500 since I bought it in July 2017. The only way I can make Snapbridge work more than once and get rid of the bluetooth greyed out issue is to do a 'reset all settings.'
This of course is infuriating since I like my D7500 set up the way I want it and I don't really want to have to fiddle with all the settings every time I want to use Snapbridge.
This problem is born of my Macbook Pro deciding it doesn't like its USB or SD card ports any more, so I am now forced to download to my phone and then sync it to the Mac. Talk about a flippin work around.
Why why why won't Nikon sort this problem out? It sees just about every one of their cameras suffers the same problem.
Come on Nikon, get your $$$$$ together or this Nikon enthusiast will start looking at Canons.......AGAIN!!!