Hi Tony,
The actual image sizes are set in your WooCommerce settings. In the Woo settings screen, click on Products and then Display. The image sizes are set at the bottom of that screen.
The category images will be the “Catalog” ones and the individual item ones are the “Single Product Images.”
Any changes made to the image sizes will only affect images uploaded after the changes were made. To change images that have already been uploaded you need to install and run the regenerate thumbnails plugin.
Looking at the screenshot, if the images are sized the same before being uploaded, it would appear that the left two images were uploaded under a different catalog image size than the one on the right. That would cause them to have different sizes even though the source files were the same dimensions.
Try adjusting the catalog image size and then run the regenerate thumbnail plugin and see how it works for you.
Let me know how it goes,
Bill