The problem occuour when the source files are 32bit format.
Somehow you need to change from 32bit to 24 or 16bit before you create new MultiTrack song in uTool.
There’s a free audio editor application: https://audacityteam.org/
With this application you need to open your 32 bit wav files(s) then click on the File/Export tab and select wav (16 or 24bit) for output format from the drop down menu.
Use this file(s) to create new multitrack song in the uTool, then re-export your song(s) from the uTool to your USB storage.