The problem might be in the generate_samples() generator: This yields only 1024*8 (=8192) samples. If I replace the line

for i in range(1024*8):

by

while True:

so that an infinite amount of samples is generated, your example works on my machine.

The problem might be in the generate_samples() generator: This yields only 1024*8 (=8192) samples. If I replace the line

for i in range(1024*8):

by

while True:

so that an infinite amount of samples is generated, your example works on my machine.

Since generate_samples() only yields 8192 samples, train_batches_stream only yields 32 batches of 256 samples each, so that you can only train for at most 32 steps. However, you ask for 2000 steps.