Despite the overfill, there is still a hole in this bar. As the soap was cooling and contracted in volume, the soap shrunk up, leaving a hole as bubbles drifted to the top of the surface. In this case, the bubbles caught at the top of the mold and became more concave as the soap shrunk. To help prevent this, tap your mold several times on the counter right after you’ve poured the warm soap. This will force the majority of air bubbles to the top of the mold and out the spout.
Watch for a post later today about trimming and finishing your 3-D soaps.