Why does my sourdough, spelt bread have a horizontal hole through the whole loaf after baking? It runs roughly ⅔ from the bottom. Looks great until it's sliced!
This is one possibility, that there is a layer of flour that prevents the dough from welding after shaping. This also includes air that expands during baking and causes the layers to separate.
Another possibility , if it is not flour causing the problem, is that the dough hydration is too low and that also can cause problems with the dough being able to weld. Drying of the surface of the dough can give a similar effect.
If it is not a problem from either of thes causes, then it may be just that when you are shaping your loaf, you are trapping big pockets of air so your shaping technique might require some attention. This is best done by a rolling action rather than a folding action to minimise the chances of this sort of thing happening. There are lots of videos and guides out there and SourDom gives a good description in his Beginners Blog an this site.
Good luck with your projects.