I’ve had this issue too. I’m not sure what the cause is. But I seem to be able to get rid of the gaps if I go into Gallery > Manage Gallery > (click on the gallery you want to change) > Sort Gallery. Once you’re in the sort gallery area, you can drag and drop them into new locations. For what ever reason (no logic that I can make out) just rearranging the images can shift the gaps around. And if you happen to land on an arrangement that the plugin arbitrarily deems worthy. For no reason at all, all of the sudden it works and the gaps disappear. Clearly that’s not a real fix. But I figured I’d share anyway.
