Nikon D810 Not Recognized

I have a new MacBook Air running El Capitan.

My Nikon D810 is rarely recognized by Apple's own Image Capture. (I got Capture One to recognize the camera once, but only once.)

No problem on my 2012 iMac and Image Capture.

Is this problem with El Capitan or with the USB ports on the MacBook Air?

Thank you!