DJM900 sound cut off with traktor after a few hours of work.

Hey
So I had this weird problem yesterday.
Let me tell you about my setup first:
I have 2 MacBook Pro, Both late 2011 (not Retina Display)
The main Macbook is connected to DJM900 as a soundcard and 2xCDJ-2000 via Powered USB hub.
The 2nd Macbook is connected to Rane SL3 as timecode backup - RCA/Line inputs.
Also, I have SD Card inserted to one of the CDJ's and LAN cable connected between them (LINK) - connected to the DIGITAL inputs of the mixer.

DJM900 manufacturer date is Dec 2014
CDJ2000's - Jan 2015

After working for 4 hours approx, I disconnected and reconnected my headphones (Sennheiser HD-25). when I reconnected them - the sound from the DJM900 Audio card stopped and no signal was coming out of the main outputs. Traktor continued to work as usual. In that point I went to my backup MAcbook to play some music from Serato ScratchLive, that i noticed that the software says "hardware disconnected" although it was connected ! I immediately played something from my SD card through the digital inputs, while playing from the digital inputs I disconnected and reconnected the USB on the DJM900 and everything worked again without any problems. also, Serato suddenly recognized the soundcard and went back to Timecode mode ..

Do you have any Ideas how to work it out?
Thanks
Udi