decoder generates noise images

Hi,

I am trying to train a decoder on CUB-200 dataset. However, after nearly 400 epochs, the decoder can still only generate noises and I have been trying a long time to figure out why. I would appreciate your suggestions!

So the training loss decreases pretty steadily, but the images still look like this:

I have only used 1 unet and the configuration is: dim = 128, image_embed_dim = 768, dim_mults = (1, 2, 4, 8),, for the decoder, the parameters are: image_size=64, timesteps = 1000, image_cond_drop_prob = 0.1, text_cond_drop_prob = 0.5, learned_variance = False.

Thank you!