I think it’s a routing problem.
1/2 are your main stereo in/outs, and it looks like they’re getting mixed up with 3/4 when I trace through that diagram.
If you look at the System input/output menu, you’ll see 1/2 as a stereo pair, and it will automatically handle mono or stereo from those connections.
3 and 4 are two isolated ins and outs, but they can be used as a left-right stereo insert loop if you match up 3to3 in/out and 4to4 in/out.
So your main stereo input and stereo output are best done on 1/2, and your FX loop via 3/4.
That should help, I think.
