Perte De Son Dans Pro Tools, ou sont passes tous mes dB??? Options

[StereoDeck]

Hello. For my first post i'm asking for help:

My system:
Mix + (1Core/1Farm)
1. 888-24 io (on the core)
1. Adat Bridge (not the 24) on the farm connected with the Y
2 Adats connected with lightpipe to the adat bridge.

Pro tools TDM 6.4.1
Mac os X.3.9
G4 QS 933 1Go Ram

Now the issues:
I am working on a 50 tracks Mix. 24 outs to the mixers.
I have both Stereo and Mono Tracks.
Randomly, i have a loss of signal on some outpouts. about 14db
for example:
i have 4 tracks of kick routed to the 1 output (888) and 4 tracks of snare to outpout 2. Everything was fine i was almost hitting red on the 888 vu meters for out 1&2. Now it stalls below the yellow. And i didn't change anything.
and, when i create a master fader for out 1&2 it shows the same than on the 888 whereas the vu of the tracks are hitting red.

Worse: new session, only one track. No audio just a signal generator set to 0db (tracks hits the red) on the 888: not even yellow. If i check the master out for 1&2: ok with the 888 Leds: not even yellow.
And the best: if i route the track in a aux and route the aux to the out 1&2 i loose again for almost 8dB on both the master bus and the 888 vu :confused:

now what i tried:
Change the interfaces: i put the adat bridge ont the core and the 888. I have the same trouble but now on the adat #1 (correspond to the out A1 & A2 in the soft)
So i guess the interfaces are not involved neither the digicables.
It can only come from the mix core (but i doubt) or The soft itsfelf.
oh i also try to do it with no plugs... same result

it was even worse yesterday since several outputs had the same issues.
When i came back this morning all worked ok util now.

I wonder if it can be a problem using mono out and stereo outs at the same time...

i restarted everything thousands time. i don't know.

Thanks for your help