Okay, I have singled out the problem: It is my Thief's Cuirass. The names for the files are:
Thief'sCuirass.json
Thief'sCuirass.png
Thief'sCuirass_Arms.png
Thief'sCuirass_Body.png
Thief'sCuirass_Female_Body.png
And here is the code for the .json:
{
"displayName": "Thief's Cuirass",
"size": [30, 20],
"maxStack": 1,
"value": [0,8,0,0],
"rare": 3,
"tooltip": "A protective and light cuirass used by thieves.",
"defense": 5,
"armorBody": true,
"hasHands": true,
"setName": "Thief",
"recipes":
[{
"items": {"Bunny": 5, "Squirrel": 5, "Iron Bar": 4},
"tiles": ["Anvil"],
"creates": 1
}]
}