As far a I know, stereo channels are only sent to LR in a LCR set-up. FX returns are stereo. Would suggest to check L or R signal.
https://iliveforum.allen-heath.com/topic.asp?TOPIC_ID=2147&SearchTerms=stereo,LCR
Wouter
IDR32, R72, Dante, Mixpad
laptop, TP-Link TL-WR1043ND
