I've tested this repo with my own 360 degree images successfully, for getting a better colored mesh model, i will suggest:

1. use FULL resolution photos to run COLMAP and imgs2poses.py file, like 3968*2976, make sure you take photos horizontally ;

2. if you can't see your center object clearly when you run the extract_mesh.py file, probably your poses_bounds.npy file is not right, check this file with np.load('poses_bounds.npy')[:, -2:] to see whether there are many small values or not, make sure these array values at normal level ;
   (by the way, if you've trained a good model, you will not have this problem)

3. a good model should converge to psnr 25 in the first 10k steps, if not then something is problematic ;

4. when you tune the xyz range and sigma_threshold parameters to get a better volume box, start with (x_range, y_range=-1.5,1.5, z_range=-4, -1, sigma_threshold=5) , cause i found the object always at a lower place, make sure you can see your object completely and clearly, then it will be easy for you to tune these parameters slightly to get a better result.

Thanks for the author's help, i've solved many problems, so i want to post my advices here for those people who have the same problems.

Finally, i can show you my colored mesh model, it turns out this repo is good for 3D reconstruction: