This weekend my CDJ told me to "wait"...forever apparently.

Some information which might help, as I think it is related. But I am not a Expert, but until now I never failed in finding a workable solution..

Today I tried to 'freeze' my CDJ just for testing purposes. I had a similar experience,   know how to reproduce, so your question might be related to my findings (not 100% sure).

I use CDJ2000Nxs with a Macbook Pro - 100 mbit wired. External HD connected to the Macbook, not to the CDJ (just for testing).

When I shortly released the RJ45 connector to break the connection at the back of the CDJ (on purpose), the CDJ will go into the emergency loop. This is okay, so lets try to revive the CDJ. Turn power of, wait a few seconds, power on, wait until network settings are correct.

At this moment my deck will go into the 'wait until you weigh an ounce mode'. Offcourse the broken connection to the Rekordbox database might be the cause of this 'Wait'. See:  https://www.youtube.com/watch?v=UkxUf7P-dPA. 

The other deck responds perfectly but to have 2 working decks again, I had to close Rekordbox, restart the external HD / rekordbox and I can use the set again.

To put this to your situation: there might have been a very small error in the wireless transmission. Too short to trigger the Emergency Loop, but long enough to loose connection to the database/card/rekordbox. If the SD cards were in the CDJ's, a tiny connection error to Rekordbox could still be the problem (for example if the CDJ has priority to regain access to the database, which flooded the connections to the database)

I understand that the setup could work wireless, but is it possible to try it wired the next time? Just to see if the problem has something to do with this. Wireless connections are getting more and more problematic due to growing use  of the wireless bandwith. Every telephone at your performance could have Wireless turned on. Even without connecting, this could have an effect on your connection. It takes away precious bandwith...

I am a big fan of wireless, but I don't use this in my performances... just to be sure...

Thanks Fabian.  I'll give the wired connection a shot but I've been using the wireless connection both to rehearse and perform in NYC for just under a year now and never encountered this problem.  I have to believe interference in Manhattan is about as bad as it gets.  

Hi Fox, it is just to find a 'source' for the problem, I think the Rekordbox database is not that forgiving when it looses connection.

The thing which surprised me: I switched off the CDJ and the unit came back with a 'Wait' icon. I expected the unit not to be able to connect to the songs from the macbook, but I didn't expect it be in this loop. In this situation you cannot easily go back to SD or USB for backup / emergency. Restarting Rekordbox isn't allways fun during a performance ;-).