Rekordbox problem with CDJ 2000 Nexus

At random times, when I play tracks on the CDJ 2000 Nexus through the Rekordbox software by the DJ Link, the CDJs goes into Emergency Loop and says some fucntions are limited.

The CDJs are connected to a powered ethernet hub where a DJM 900 Nexus is also conneceted. From there they go into i powered dock and into a USB 3.0 port on my Macbook pro.

I have tried to restart the CDJs but then Rekordbox can't connect to them through DJ Link. Not untill I have restarted the Macbook.

There's no ethernet port on the Macbook, so I can't connect it directly to the CDJs.

Any ssuggestions on what might be wrong?

It's a fairly new macbook, and the dock is a Kanex Simple Dock.