Really strange isn’t it!
Thanks it works great and gives the same image as what I was seeing with my more crude method, thanks!
I’ve noticed in default_fits_loader  you have left a space for a custom label function. Would it be possible to alter the loader so that instead of loading single fits files, it would load a stacked fits data cube, split the 2d arrays and assign them the labels?
This would help to save a lot of space by saving cubes instead of lots of fits files in preprocessing.