UR-RT4 - No signal through line inputs!

Hi all! I hope you can help me with this.

I regularly use the UR-RT4 to record through analog outboard equipment by outputting from line outputs 3/4, through the outboard gear, and back into line inputs 5/6.

The outputs work fine, but suddenly I can’t get a signal from the line inputs! Input 3 through 6 are all dead quiet when running line level (preamps are working).

I’m not seeing or hearing any levels in the dspMixFx software and nothing in my DAW.

I’ve checked my connections and routing thoroughly and tried different setups in dspMixFx.

Any ideas what could be causing this?