Barrier Coat/Paint Cracks
I can't really get a good idea of what's going on from your pictures, but I believe Barrier coat is dark grey. It should always be applied to the hull before any bottom paint is applied. If applied right, barrier coat really shouldn't slough off in chunks.
I can't really tell if you have barrier coat or not, but an easy test is to take a pocket knife and gently scrape off bottom paint until you get to the hull, if you come to a hard, dark grey coating just before the hull, it's probably barrier coat. I haven't seen regular bottom paint grey in color.
Others will probably have a better test, but that's what I do.