A4 output drops when internal and input play at same time

Hey there, weird issue here - I’ve got the A4 receiving an oscillator from my modular on the left input. It’s routed through track three (Osc1 set to L), and the sound is coming out the main outs fine. However, when I bring in internal track one playing a two note chord, the output volume drops significantly. Mute track one and the volume of the input L oscillator fades quickly back up to full volume. Any ideas what’s going on here? It’s driving me bonkers…

so quiet here…so cold…

I know I might say something obvious here - but does this happen also if you play only one note from track one? Just to exclude polyphony being the culprit with the voice allocation algorithm “stealing” the voice from track 3.