WARNING:tensorflow:Gradients do not exist for variables ['conv4_3/bias:0',...] when minimizing the loss.

[jessicametzger]

I am using ssd_keras with tensorflow2 backend to train the ssd300 model (using this ssd_keras_tf2 repository) and everything "works," except I keep running into this error when I start training:

WARNING:tensorflow:Gradients do not exist for variables ['conv1_1/bias:0', 'conv1_2/bias:0', 'conv2_1/bias:0', 
'conv2_2/bias:0', 'conv3_1/bias:0', 'conv3_2/bias:0', 'conv3_3/bias:0', 'conv4_1/bias:0', 'conv4_2/bias:0', 'conv4_3/bias:0', 
'conv5_1/bias:0', 'conv5_2/bias:0', 'conv5_3/bias:0', 'fc6/bias:0', 'fc7/bias:0', 'conv6_1/bias:0', 'conv6_2/bias:0', 
'conv7_1/bias:0', 'conv7_2/bias:0', 'conv8_1/bias:0', 'conv8_2/bias:0', 'conv9_1/bias:0', 
'conv4_3_norm/conv4_3_norm_gamma:0', 'conv9_2/bias:0', 'conv4_3_norm_mbox_conf/bias:0', 'fc7_mbox_conf/bias:0', 
'conv6_2_mbox_conf/bias:0', 'conv7_2_mbox_conf/bias:0', 'conv8_2_mbox_conf/bias:0', 'conv9_2_mbox_conf/bias:0', 
'conv4_3_norm_mbox_loc/bias:0', 'fc7_mbox_loc/bias:0', 'conv6_2_mbox_loc/bias:0', 'conv7_2_mbox_loc/bias:0', 
'conv8_2_mbox_loc/bias:0', 'conv9_2_mbox_loc/bias:0'] when minimizing the loss.

They ran into the same thing when porting to tf2 in ssd_keras_tf2. Moreover, most parameters aren't changing, and the loss doesn't change after the first couple steps.

System Info

• Ubuntu 20.04.1
• tensorflow-gpu 2.2.0
• keras: using tf.keras through tensorflow-gpu
• Which commit: latest commit of ssd_keras_tf2 (the error also happens when I manually change the latest ssd_keras code to use tf.keras with tf2 backend)
• GPU: NVIDIA Corporation TU104GL [Quadro RTX 5000] (the error happens whether I am running on gpu or cpu)

Full error message

Epoch 00001: LearningRateScheduler reducing learning rate to 0.001.
Epoch 1/120
WARNING:tensorflow:Gradients do not exist for variables ['conv1_1/bias:0', 'conv1_2/bias:0', 'conv2_1/bias:0', 'conv2_2/bias:0', 'conv3_1/bias:0', 'conv3_2/bias:0', 'conv3_3/bias:0', 'conv4_1/bias:0', 'conv4_2/bias:0', 'conv4_3/bias:0', 'conv5_1/bias:0', 'conv5_2/bias:0', 'conv5_3/bias:0', 'fc6/bias:0', 'fc7/bias:0', 'conv6_1/bias:0', 'conv6_2/bias:0', 'conv7_1/bias:0', 'conv7_2/bias:0', 'conv8_1/bias:0', 'conv8_2/bias:0', 'conv9_1/bias:0', 'conv4_3_norm/conv4_3_norm_gamma:0', 'conv9_2/bias:0', 'conv4_3_norm_mbox_conf/bias:0', 'fc7_mbox_conf/bias:0', 'conv6_2_mbox_conf/bias:0', 'conv7_2_mbox_conf/bias:0', 'conv8_2_mbox_conf/bias:0', 'conv9_2_mbox_conf/bias:0', 'conv4_3_norm_mbox_loc/bias:0', 'fc7_mbox_loc/bias:0', 'conv6_2_mbox_loc/bias:0', 'conv7_2_mbox_loc/bias:0', 'conv8_2_mbox_loc/bias:0', 'conv9_2_mbox_loc/bias:0'] when minimizing the loss.
WARNING:tensorflow:Gradients do not exist for variables ['conv1_1/bias:0', 'conv1_2/bias:0', 'conv2_1/bias:0', 'conv2_2/bias:0', 'conv3_1/bias:0', 'conv3_2/bias:0', 'conv3_3/bias:0', 'conv4_1/bias:0', 'conv4_2/bias:0', 'conv4_3/bias:0', 'conv5_1/bias:0', 'conv5_2/bias:0', 'conv5_3/bias:0', 'fc6/bias:0', 'fc7/bias:0', 'conv6_1/bias:0', 'conv6_2/bias:0', 'conv7_1/bias:0', 'conv7_2/bias:0', 'conv8_1/bias:0', 'conv8_2/bias:0', 'conv9_1/bias:0', 'conv4_3_norm/conv4_3_norm_gamma:0', 'conv9_2/bias:0', 'conv4_3_norm_mbox_conf/bias:0', 'fc7_mbox_conf/bias:0', 'conv6_2_mbox_conf/bias:0', 'conv7_2_mbox_conf/bias:0', 'conv8_2_mbox_conf/bias:0', 'conv9_2_mbox_conf/bias:0', 'conv4_3_norm_mbox_loc/bias:0', 'fc7_mbox_loc/bias:0', 'conv6_2_mbox_loc/bias:0', 'conv7_2_mbox_loc/bias:0', 'conv8_2_mbox_loc/bias:0', 'conv9_2_mbox_loc/bias:0'] when minimizing the loss.
WARNING:tensorflow:Gradients do not exist for variables ['conv1_1/bias:0', 'conv1_2/bias:0', 'conv2_1/bias:0', 'conv2_2/bias:0', 'conv3_1/bias:0', 'conv3_2/bias:0', 'conv3_3/bias:0', 'conv4_1/bias:0', 'conv4_2/bias:0', 'conv4_3/bias:0', 'conv5_1/bias:0', 'conv5_2/bias:0', 'conv5_3/bias:0', 'fc6/bias:0', 'fc7/bias:0', 'conv6_1/bias:0', 'conv6_2/bias:0', 'conv7_1/bias:0', 'conv7_2/bias:0', 'conv8_1/bias:0', 'conv8_2/bias:0', 'conv9_1/bias:0', 'conv4_3_norm/conv4_3_norm_gamma:0', 'conv9_2/bias:0', 'conv4_3_norm_mbox_conf/bias:0', 'fc7_mbox_conf/bias:0', 'conv6_2_mbox_conf/bias:0', 'conv7_2_mbox_conf/bias:0', 'conv8_2_mbox_conf/bias:0', 'conv9_2_mbox_conf/bias:0', 'conv4_3_norm_mbox_loc/bias:0', 'fc7_mbox_loc/bias:0', 'conv6_2_mbox_loc/bias:0', 'conv7_2_mbox_loc/bias:0', 'conv8_2_mbox_loc/bias:0', 'conv9_2_mbox_loc/bias:0'] when minimizing the loss.
WARNING:tensorflow:Gradients do not exist for variables ['conv1_1/bias:0', 'conv1_2/bias:0', 'conv2_1/bias:0', 'conv2_2/bias:0', 'conv3_1/bias:0', 'conv3_2/bias:0', 'conv3_3/bias:0', 'conv4_1/bias:0', 'conv4_2/bias:0', 'conv4_3/bias:0', 'conv5_1/bias:0', 'conv5_2/bias:0', 'conv5_3/bias:0', 'fc6/bias:0', 'fc7/bias:0', 'conv6_1/bias:0', 'conv6_2/bias:0', 'conv7_1/bias:0', 'conv7_2/bias:0', 'conv8_1/bias:0', 'conv8_2/bias:0', 'conv9_1/bias:0', 'conv4_3_norm/conv4_3_norm_gamma:0', 'conv9_2/bias:0', 'conv4_3_norm_mbox_conf/bias:0', 'fc7_mbox_conf/bias:0', 'conv6_2_mbox_conf/bias:0', 'conv7_2_mbox_conf/bias:0', 'conv8_2_mbox_conf/bias:0', 'conv9_2_mbox_conf/bias:0', 'conv4_3_norm_mbox_loc/bias:0', 'fc7_mbox_loc/bias:0', 'conv6_2_mbox_loc/bias:0', 'conv7_2_mbox_loc/bias:0', 'conv8_2_mbox_loc/bias:0', 'conv9_2_mbox_loc/bias:0'] when minimizing the loss.
   4/1000 [..............................] - ETA: 24:42 - loss: 1.4227

Reproducible example

The error happens whenever I call model.fit(...) or model.fit_generator(...), where model is an ssd300 model, and where the backend is tf2. It happens whether I am using cpu or gpu. E.g. when I run the ssd300_training.ipynb tutorial, I get that error.

I would really appreciate it if someone trying to use tf2 backend found a solution for this, because I'm pretty sure I'm not the only one.

[anashad]

Hello. As is suggested in this issue #359, the problem comes from the generator that yields a list instead of a tuple. You should be able to cast ret to a tuple in this line
https://github.com/IntranelConsulting/ssd_keras_tf2/blob/183d57b1989fc6d732bf1028b6323bdd5771e78a/data_generator/object_detection_2d_data_generator.py#L1174