I am experiencing ugly and critical problem that occurs randomly with my Fireface 400.

Problem description:
I am sending stereo audio signals to 3 software outputs in ableton 1-2, 3-4, 5-6
In RME totalmix each of this software outputs are routed to corresponding analog outputs of RME card 1-2 to 1-2, 3-4 to 3-4 and 5-6 to 5-6 accordingly.
For some unknown reason analog outputs 1-2 and 5-6 are "silent" and no signal is coming out visually looking at totalmix.
This issue is reproduced not only with Ableton, so it's not about ableton. If i run some tune in Itunes it goes to software out 1-2 and if it's routed to analog out 1-2 in total mix it's just silent and no signal.

This weird behaviour happens randomly and i cant understand what triggers this, but this is critical for us as it happens when we are on tour and then it's a disaster.

May be it's not a card, but totalmix bug?

Please download the video where I show the problem :
https://drive.google.com/file/d/1yVbN5R … qur3Z/view

Sys info:
MAC OS Sierra 10.12.6
RME Fireface 400 with latest firmware and driver installed
Device is powered with proper external power supply 

Any suggestions on how to fix / what to fix?

Tnx