@aitzbergh hi~ maybe here is the solution way:

MP3 Conversion for WaveFlow Player
Problem: Some MP3 files may not play due to format issues.
Solution: Convert your files using FFmpeg.
Quick Steps:
1、Visit the official FFmpeg website and Install FFMpeg: https://ffmpeg.org/download.html
2、Download the Conversion Script from Github : https://github.com/musicaJack/M5Stack_Tab5_Converter/blob/main/mp3_convert.py
3、Place the Python script​ (mp3_convert.py) in the same directory with your MP3 files
4、Run the conversion script: python mp3_convert.py
5、Copy fixed mp3 files to TF Card in mp3 directory