X96max optical audio error

I have a problem with the optical audio output.
for days after installation, no problem.
then the audio will go out at random intervals for a few seconds and then come back.
now i connected a USB sound card with optical output to the amplifier, went for 3 days without any problems, now it goes out again and the sound comes back.
sound setting:
limitation to 48KHZ
Output Configuration: Most Matching
x96Max s905X2
thank you for your help