title: Training a Keras model yields multiple optimizer errors
body: <p>So I need to retrain Tiny YOLO using my own dataset. The model I am using can be found here: <a href="https://github.com/qqwweee/keras-yolo3" rel="noreferrer">keras-yolo3
  </a>.</p>
  
  <p>I started training and I get multiple optimizer errors, added the code of the errors to stop confusion.
  And I noticed the training is going slow even tho it should use the GPU, and after digging a bit I found that this is not using the GPU for training.
  I should note that on another smaller network which I used for learning training uses GPU so everything is set correctly from that side, and they are no errors of this type when I did that training.</p>
  
  <p>Is this slow and somewhat CPU training because of said errors? How can I fix this does anyone know?</p>
  
  <pre><code>Using TensorFlow backend.
  WARNING: Logging before flag parsing goes to stderr.
  2019-08-19 09:45:08.057713: I tensorflow/stream_executor/platform/default/dso_loader.cc:42] Successfully opened dynamic library nvcuda.dll
  2019-08-19 09:45:08.264577: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1640] Found device 0 with properties:
  name: GeForce GTX 1060 6GB major: 6 minor: 1 memoryClockRate(GHz): 1.8475
  pciBusID: 0000:01:00.0
  2019-08-19 09:45:08.270723: I tensorflow/stream_executor/platform/default/dlopen_checker_stub.cc:25] GPU libraries are statically linked, skip dlopen check.
  2019-08-19 09:45:08.275827: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1763] Adding visible gpu devices: 0
  2019-08-19 09:45:09.214197: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1181] Device interconnect StreamExecutor with strength 1 edge matrix:
  2019-08-19 09:45:09.217605: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1187]      0
  2019-08-19 09:45:09.219777: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1200] 0:   N
  2019-08-19 09:45:09.222399: I tensorflow/core/common_runtime/gpu/gpu_device.cc:1326] Created TensorFlow device (/job:localhost/replica:0/task:0/device:GPU:0 with 4712 MB memory) -&gt; physical GPU (device: 0, name: GeForce GTX 1060 6GB, pci bus id: 0000:01:00.0, compute capability: 6.1)
  Create Tiny YOLOv3 model with 6 anchors and 80 classes.
  Load weights model_data/tiny_yolo_weights.h5.
  Freeze the first 42 layers of total 44 layers.
  Train on 8298 samples, val on 922 samples, with batch size 32.
  Epoch 1/50
  2019-08-19 09:45:19.742610: E tensorflow/core/grappler/optimizers/meta_optimizer.cc:502] shape_optimizer failed: Invalid argument: Subshape must have computed start &gt;= end since stride is negative, but is 0 and 2 (computed from start 0 and end 9223372036854775807 over shape with rank 2 and stride-1)
  2019-08-19 09:45:19.781035: E tensorflow/core/grappler/optimizers/meta_optimizer.cc:502] remapper failed: Invalid argument: Subshape must have computed start &gt;= end since stride is negative, but is 0 and 2 (computed from start 0 and end 9223372036854775807 over shape with rank 2 and stride-1)
  2019-08-19 09:45:19.935930: E tensorflow/core/grappler/optimizers/meta_optimizer.cc:502] layout failed: Invalid argument: Subshape must have computed start &gt;= end since stride is negative, but is 0 and 2 (computed from start 0 and end 9223372036854775807 over shape with rank 2 and stride-1)
  2019-08-19 09:45:20.168936: E tensorflow/core/grappler/optimizers/meta_optimizer.cc:502] shape_optimizer failed: Invalid argument: Subshape must have computed start &gt;= end since stride is negative, but is 0 and 2 (computed from start 0 and end 9223372036854775807 over shape with rank 2 and stride-1)
  2019-08-19 09:45:20.205304: E tensorflow/core/grappler/optimizers/meta_optimizer.cc:502] remapper failed: Invalid argument: Subshape must have computed start &gt;= end since stride is negative, but is 0 and 2 (computed from start 0 and end 9223372036854775807 over shape with rank 2 and stride-1)
  258/259 [============================&gt;.] - ETA: 3s - loss: 41.82962019-08-19 10:01:51.053474: E tensorflow/core/grappler/optimizers/meta_optimizer.cc:502] remapper failed: Invalid argument: Subshape must have computed start &gt;= end since stride is negative, but is 0 and 2 (computed from start 0 and end 9223372036854775807 over shape with rank 2 and stride-1)
  2019-08-19 10:01:51.138957: E tensorflow/core/grappler/optimizers/meta_optimizer.cc:502] layout failed: Invalid argument: Subshape must have computed start &gt;= end since stride is negative, but is 0 and 2 (computed from start 0 and end 9223372036854775807 over shape with rank 2 and stride-1)
  2019-08-19 10:01:51.243888: E tensorflow/core/grappler/optimizers/meta_optimizer.cc:502] remapper failed: Invalid argument: Subshape must have computed start &gt;= end since stride is negative, but is 0 and 2 (computed from start 0 and end 9223372036854775807 over shape with rank 2 and stride-1)
  259/259 [==============================] - 1078s 4s/step - loss: 41.8008 - val_loss: 35.7122
  </code></pre>