Graph disconnected: cannot obtain value for tensor Tensor Input Keras Python

This is where your graph is disconnected (uconv2 is not defined when you are calling it):

# 32 -> 64
deconv2 = Conv2DTranspose(start_neurons * 2, (3, 3), strides=(2, 2), padding="same")(uconv3)
uconv2 = Conv2D(start_neurons * 2, (3, 3), activation="relu", padding="same")(uconv2)

What fixed this graph error for me was changing this:

x_in = Input(shape=(10,), name="InputLayer")
_ = order2_embs_model(x_in)
...
model = Model(inputs=x_in, outputs=Y, name='DeepFFM') 

to this:

model = Model(inputs=order2_embs_model.inputs, outputs=Y, name='DeepFFM')