It's wrong to use a MIXER. A MIX should be used.
Your previous (and current design) has 4 signals (2 inputs + 2 pitch shifters) feeding back into a single input (MULTISHIFT); that's too much. With hi levels in the MIXER channels you saturate the audio and kill the signal.
You should not use a multishift w/ a mixer. A true stereo path should be used instead, using 2 separate single voice multishifters ot 2 pitch shifter modules.
Check my fix!
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