Not sure what your queston is. Maybe this could be an answer: The mixers always keep the last settings and if you have selected USB as input source for channels, they will be selected after a powering off and on. It's not to expect that the channels "change" their input source.
"It is not necessary to create a scene for your StudioLive in order to preserve ist settings when you power it down. The StudioLive takes continuous snapshots of the current position of every parameter on the mixer and stores them to memory every 3 seconds."
StudioLive_Series_III_OwnersManual_V6_EN_10062019, section 9.6.6 "AutoStore"