Hi Todd,
If you go to the back panel of the FX3 and FX4 units, do you have them set for ‘Mix -> Return’ fed from the FX3 and FX4 busses?
Any of the FX units can be used either being fed by an FX bus, a mix bus or a channel and routed back to the FX return channels OR they can be used inserted on a channel.
So one thing that could catch you out would be loading a show that was made on a Qu-16 (which has two FX busses) onto any other model (which have 4 FX busses).
Hope this helps, but if you’re still having trouble, you can contact us using support.allen-heath.com and maybe send through a show so we can check it out here.
Cheers,
Keith.