Some time ago there was a discussion about
, Kicad output it assembly position file with one standard and JLCPCB use other.
Practical saying, some elements present a 90 degree rotation. Last time that I used, I manually edit the position file.
About the component list / BOM I added the LCSC cost column at KiCost (New KiCost release - #13 by marcos), the components distributor used by Jlcpcb.