A mystery 300px image size
Updated Answer After doing more testing, the 300px size only gets generated when I have the official WooCommerce Brands plugin activated. So 300px is the default WooCommerce image size when the standard sizes go undefined. See wc_get_image_size() in \includes\wc-core-functions.php. It seems that at some point WC must have filled in the blank of a missing … Read more