Mixcraft 9 Pro Studio's "Convert Audio to MIDI" feature can sometimes produce a single MIDI note instead of a melody. If it happened to you, try this:
Before you convert it to MIDI, view the audio clip on Mixcraft's Sound tab, and display it in Melodyne, then click on Melodyne's Algorithm menu, and change the setting to Melodic.
Once that's done, go ahead and convert it to MIDI again.
What's happening is that Melodyne can falsely interpret an audio clip as percussive instead of melodic once in a while.