I had the exact same problem (music stuttering when playing from sd) and found the cause. I have an 128gb sd card and made the mistake of formatting it with my phone. The phone formats as fat32. That doesn't play well with 100gb music apparently. The only music player I found that worked is foobar2000. Now, I reformatted the sd card with pc to exfat, and my music plays flawless with every music player now.