I had the same issue. Here are some tips that helped me.
1. In the WOOCOMMERCE>Settings in the catalog tab, first make sure your settings for Catalog Images and Single Product Image (at the bottom of the page under image options) are at 540 width and the height would be whatever your dimension ratio allows. So for example if your uploaded images are all at 1080 width by 900 height, then the height would be 450. The best way to figure this out is to take the image you want to upload (provided that they are large format) and open it up in photoshop (or whatever photo editing software you have) Once you have it in the software simply resize the image while making sure the ratio is locked. From here just type in 540 width and walah! your height will calculated. Enter that height into the catalog tab settings along with the 540 width.
2. Once you entered those fields in, make sure your get the regenerate your thumbs plugin. Regenerate all of the thumbs and you should be set!
