Moonshine author here: The warning is from Keras library, and is benign. If you didn't get any other output, it was probably because the model thought there was no speech (not saying there really was no speech). We uploaded ONNX version that is considerably faster than the Torch/JAX/TF versions, and is usable with less package bloat. I hope you would give it another shot.
I met Bram in the Google Mountain View office. We chatted for over two hours. He was full of humility and curiosity and more interested in what I was working on (I was working on DistBelief back then). Hats off to a life full of impact and a legacy that will continue to impact programmers all over the world. RIP.