Tape out into interface showing up as mono?

Using a 1979 Peavey Mark III, focusrite 18i20 first or 2nd gen, and cockos reaper. I have the tape out going into a single channel on the focusrite. I have two of the mixer’s channels panned hard left/hard right but it’s mono in the track on reaper. I swear it has given me a stereo image on the single input/single track before, what am I doing wrong? And yes the cable is stereo.