Good day, dear DoriTos Nacho, To solve the backpack sprite penetrating the front of the character,
Just open :
luafiles514\lua files\spreditinfo\2dlayerdir_f.lub
and remove
[SPRITE_ROBE_IDs.ROBE_WINGS] = LAYER_BIG,
[SPRITE_ROBE_IDs.ROBE_BAG_OF_ADVENTURER] = LAYER_SMALL,
[SPRITE_ROBE_IDs.ROBE_WINGS_OF_FALLEN_ANGEL] = LAYER_BIG,
[SPRITE_ROBE_IDs.ROBE_AMISTR_BAG] = LAYER_SMALL,
[SPRITE_ROBE_IDs.ROBE_Love_Dad_Wings_2012] = LAYER_BIG,
[SPRITE_ROBE_IDs.ROBE_KIRIN_WING] = LAYER_BIG,
[SPRITE_ROBE_IDs.ROBE_Ribbon_Piamat] = LAYER_SMALL
it will fix your problem.
I had the same issue once with the cat fork sprite, and i managed to solve editing that file.