Shape mismatch error in route layer on specifying input shape in single_image.py

[shivamkhare95]

I specified the input shape in single_image.py :
inputs = Input(shape=(416, 416, 3))

This gave me following error:
File "single_image.py", line 11, in
outputs, config = darknet_base(inputs, include_yolo_head=False)
File "/vol1/dbstore/orc_srib/n.hri/Hand_Localization/Experiments/005_yolov3_tflite_pc/YOLOv3/darknet.py", line 67, in darknet_base
x, layers, yolo_layers, ptr = _build_route_layer(x, block, layers, yolo_layers, ptr)
File "/vol1/dbstore/orc_srib/n.hri/Hand_Localization/Experiments/005_yolov3_tflite_pc/YOLOv3/darknet.py", line 224, in _build_route_layer
x = Concatenate(axis=3)(selected_layers)
File "/vol0/tool/ml/cuda9/.venv/py2/tensorflow-1.10.0/lib/python2.7/site-packages/tensorflow/python/keras/engine/base_layer.py", line 728, in call
self.build(input_shapes)
File "/vol0/tool/ml/cuda9/.venv/py2/tensorflow-1.10.0/lib/python2.7/site-packages/tensorflow/python/keras/utils/tf_utils.py", line 148, in wrapper
output_shape = fn(instance, input_shape)
File "/vol0/tool/ml/cuda9/.venv/py2/tensorflow-1.10.0/lib/python2.7/site-packages/tensorflow/python/keras/layers/merge.py", line 392, in build
'Got inputs shapes: %s' % (input_shape))
ValueError: A Concatenate layer requires inputs with matching shapes except for the concat axis. Got inputs shapes: [(None, None, None, 128), (None, 26, 26, 256)]

I can't think of a reason as to why it is able to get shape of one layer only in route layer and not the other.