Frisian Black Bread from The Rye Baker

My brother, Aaron, and I are both enthusiastic amateur rye bread bakers. Since we live on opposite sides of the country, we often exchange pictures and messages about our bread baking adventures, and occasionally we like to bake the same recipe to compare results.
A few weeks ago, Aaron baked Frisian Black Bread from The Rye Baker twice in the same week. He couldn't get the dough to rise very far in the final proofing stage and ended up with dense loaves both times.