Mono files converting to stereo when imported

I have some students in an audio production class who are using audacity. I’m more familiar with Pro Tools and Audition. They’re encountering a strange problem. Their recordings made with Marantz field recorders are mono, 16 bit, WAV files. When the files are dragged into a mono audacity track or when they import through the menu bar, the tracks are created as stereo tracks. I don’t know if the students are using High Siera but I don’t think so. When one of the students converted the track back to mono in Audacity the track played at a slower speed.

Is there something we need to fix in the settings so the mono track will import as a mono track?

Is there a reason why the conversion back to mono would produce a track playback at a slowed down speed?

Thanks in advance for any help with this issue.

Which Audacity?

Right click or control-click one of the files > Get INFO. Is it what you think it is? What’s the sample rate? 48000?

Create a 10 second test clip of any sound from one of those recorders (read the milk carton) and post it on the forum. Scroll down from a forum text-entry window > Upload attachment.