First off, I cannot get the MOD UI to work - so that may be a seperate issue…
BUT! just adding an audio fx layer and using the stereo mixer to pan all the incoming audio from the LEFT side of the stereo input through an effects chain that then is routed via another stereo mixer (with the right input, output and the mid levels all turned down) to the LEFT output - so far so good! Audio passes from the left to the left, no audio from the right is heard
NOW! adding a second audio fx layer, with the intention of routing audio from the RIGHT side of the stereo in (essentially I want a 2 channels of separate effects) as a separate layer via a stereo mixer inserted in this chain, this time with the left input and output and mid turned down, you would think this would work! BUT! This time, the audio is routed into the other effects chain, nothing I can do on the mixer changes that. I can turn down all the faders, audio still goes into the first effects layer.