Copying music cassettes to CDs

My computer and its version is Mac OS Sierra, Ver. 10.12.4. The version of Audacity is 2.1.3.
I am copying music cassettes to CDs. I use a Cassette2USB Converter. Many of the cassettes transfer very well to the CDs. Others, however, do not play back satisfactorily. During playback I can hear both sides of the cassette tape simultaneously. I can convert one cassette to a CD and it works fine. But the next one I convert may be the one on which I can hear both sides of the tape at once.

Can you tell me what is happening and how to correct it?

Kenneth W. Theis
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Plug headphones into the cassette player for the second side or tape to make sure it is not a problem with the tape reproduction.

If not, and the first recording is still present in Audacity, press Solo on the track for the second recording so that you only hear that track. And when you export, use File > Export Multiple… and export based on tracks.