vaxnerf can not reach convergence

[YuiNsky]

this can give a coarse result after 2500 step
python train.py
--config configs/demo
--data_dir data/nerf_synthetic/lego
--train_dir logs/lego_c64f128
--num_coarse_samples 64
--num_fine_samples 128
--render_every 2500

but using voxel to train can not reach convergence
python train.py
--config configs/demo
--data_dir data/nerf_synthetic/lego
--voxel_dir data/voxel_dil7/lego
--train_dir logs/lego_vax_c800
--num_coarse_samples 800
--render_every 2500

the result is totally a white background