Looks like the issue is in ModelBakery#loadModel, specifically, where ".json" is appended to the resource path. In 1.12.2, this was not done:
1.13.2:
iresource = this.resourceManager.getResource(new ResourceLocation(location.getNamespace(), "models/" + location.getPath() + ".json"));
1.12.2
iresource = this.resourceManager.getResource(this.getModelLocation(location));
which means you should be seeing a message like:
[minecraft/ModelBakery]: Unable to load model: ':block/some_model.obj' referenced from: some_blockstate: java.io.FileNotFoundException: mod_id:models/block/some_model.obj.json
Edit:
Oops.. not entirely correct. While hat was true, seems I didn't follow the rabbit hole deep enough as getModelLocation actually does what is in 1.13.2, just with one less method.