Tin loaf - imploding sides

Toast

I wonder if anyone can help...I've baked a sandwich loaf in a tin. Great oven spring and the crumb structure is also great but the side walls of the loaf have sunk/imploded somewhat. Any ideas why?

Many thanks.

If possible, please upload images of the loaf and individual slices. It will be a great benefit for those wishing to help.

Danny

So now I've cut further into it to take pictures and discovered that it has the most horrific flyaway crust - as in half the height of the loaf is a gaping chasm. Ugh, Overhydrated?