remote video sometimes become gray

Hi, I am a newer to mediasoup. I run this demo succeed and now I have a question. When I test it, I find remote video sometimes become gray. Could you help me ?
video info is as below:
codec VP8
max spatial layer: 2

I’m sorry, we cannot give technical responses based on observed behaviour in the mediasoup-demo. We wrote LOT of documentation in The mediasoup-demo is just a demo project. Everything is explained in the documentation. Look for the consumer.on('layerschange') event in server side (and not just that).