Left channel copying to right channel

Hi, I am trying to record an old magnetic reel-to-reel tape through a Behringer q802 USB mixer. It records fine to stereo track, but when I turn down the left channel knob on the mixer, both the right and left channels lose audio. I have looked online for fixes, but none seem to work. I have discovered that the problem is probably in Audacity. I checked the settings on the computer and selected my mixer to be a stereo input, but that didn’t work. Both the left and right channels are getting to Audacity, but for some reason it takes the left channel and copies it to the right channel.

Any ideas on what else to try? Do I need a driver for my mixer, or is it a bug in Audacity?

Only recording the left channel (twice) can be due to a Windows setting …

I tried that, but it still has the same problem. I’m using Audacity 3.7, would that affect it?