Ideally, mp3 is a compressed file format. When you edit and render them they become more compressed. I think this could be the reason that you're getting trouble with exported audio. You can try to use uncompressed file formats like WAV for a better editing experience.
Wave doesn't work either. I've tried so many different combinations and when editing on my phone the audio skips on export 9/10 times. This has been going on for a loooooong time. Please provide better support here. This issue has nothing to do with mp3.