It also has been stated in a QC35 thread, but wanted to make a searchable post for QC30. There is a serious compatiablility issue between my QC30s and my M720 mouse. I don't know if it is electromagnetic or software based, I also do not have a fix other then to disconnect my M720 and reconnect my MX Master. I was just happy to get my QC30s working again. I have a Logitech K850 keyboard that works fine while QC30s are connected, it's just the mouse.