Howdy
Probably your item model doesn't have "builtin/entity" as the parent type. (see the "Item" section of https://minecraft.gamepedia.com/Model)?
If that doesn't work, I'd suggest trying some breakpoints in strategic locations, eg:
- inside your lambda for supplying the ItemStackTileEntityRenderer
- inside the render method of vanilla ItemStackTileEntityRenderer
- inside ItemRenderer::renderItem(ItemStack itemStackIn ....)
However - based on your screenshots it doesn't look like you need an ISTER to render the sword. You can just use a vanilla icon (item/generated) and set the "display" parameters correctly in your item -i.e. the rotation, scaling, translation. If your icon looks similar to the sword icon, then try copying the vanilla sword item display parameters into yours.
-TGG