The dimensions seem to be different. I noticed the first 3 images are naturally sized at 1800 x 600, while the last few images that show up large in the slider are 1200 x 600. I’m wondering if that has something to do with it.
Here is a link to the first image that is being used (1800 x 1600) – http://whattherapy.com/wp-content/uploads/2016/08/Blue-in-Hand-Transforming-Grief-1800×600.jpg
Here is a link to one of the images that show up larger in the slider (1200 x 600) – http://whattherapy.com/wp-content/uploads/2016/07/Spiritual-Divorce-1200×600.jpg
This isn’t necessarily Theme related, but it has more to do with the size of the images, the slider, and the way WordPress scales images. This same thing would happen on any theme you use.
Is it possible to create a temporary login so I can take a quick look at the slider settings, as well as your image sizes?
Great looking site by the way!