• It might be surprising, but adding a tablespoon of flour to the filling will help the sugar from leaking out.• If the sugar leaks out and puddles, you'll be left with gaps in your bread.
• When you roll the dough up into a log, it should be snug but not tight.• A very tight dough can expand too quickly in the oven when it bakes, resulting in tunnels.
• Proof the dough fully until it rises just above your pan, is full of air, and passes the "finger poke test."• If the dough is under or over proofed, you may get gaps.
• Let the bread cool fully before slicing.• While tempting, slicing into a hot bread will release steam and may cause the bread to collapse. It's still baking!