When I add product image, some product images are added but some are not (no image is shown and it remain ‘blank’) but product gallery images can be added.
Because of this problem, in catalog /shop mode, not all product’s thumbnail is shown.
You have not configured HTTPS correctly. In result images are uploaded via HTTP and site is trying to work via HTTPS. Navigate to Settings and insert the address via https https://gyazo.com/0093dac7dd5c28ea74e9076347fd93f2