That’s a wonderful story, k_b.
About a year ago I was playing on stage in a large auditorium with a Celtic Folk group, me on piano, them on banjo, guitar, and fiddle, plus string bass. They were sharing one big mike, my piano had its own built-in mike. There were two monitors, one for them and one for me. I could hear them just fine in my monitor, but could not hear myself, except directly from the piano. Nothing in the monitor. They could hear themselves in their monitor, but could not hear me.
We finished the piece more or less together and asked each other how it had gone. Nobody knew.
Later we found out that the audience was getting the same feed that the others were getting on their monitor. In other words, the audience couldn’t hear me at all. My grand-daughter even asked me if I had been playing at all. She could see my hands moving, but couldn’t hear a thing.