I'm using Native Instrument's Guitar Rig 6 plug-in with Live 11 on my two Apple Macs and I'm having the following issue on both - when using the AU version I need to change the audio input channel in Guitar Rig to another channel and back for the plug-in to record or playback audio. The VST version works fine however. This occurs on both my 2017 iMac and 2015 MacBook Pro. I'm able to recreate this situation on a new Live 11 project.
My work around is simply to use the VST version of Guitar Rig 6 with Live 11 on my Macs. I've previously used AU versions of plugins on my Macs running Ableton without issue. Probably more of an issue on Native Instrument's side, but I'm curious if others experienced this?