“it happened to me twice that during the program I no longer have a signal in the speakers but only in the monitors. in both cases the signal returned after about two minutes without doing anything to it”
Check that the issue is not between the mixer and the speaker system.
Did you still show output level on the main metering?
Check and see if you still have sound at the headphone jack.
Try plugging a monitor into the main outputs and see if they have
sound if the main speakers cut out again.