I can't tell for sure, but it looks like they may have the comb off center of the frame. As if they started two combs and they met in the middle. If so, that is likely a pass through hole. They will leave them at times, especially if you were using starter strips.
When you give them new combs to draw, be sure they are tight against the next frames. The least little gap and they will draw comb beside where it is supposed to go.