Got mine working with DSTT_Launcher from here: https://gbatemp.net/threads/r4-stage2-twl-flashcart-launcher-and-perhaps-other-cards-soon%E2%84%A2.416434/
and YSMenu from here: https://gbatemp.net/threads/retrogamefan-updates-releases.267243/
Partition layout is fine. I think it's just some leftover data that didn't get overwritten after formatting, and cfw still somehow manages to use it. Format your card from windows with "quick format" unchecked, and you'll be fine.