Images become blurry & stretched images on mobile and tablet device

Recently I just found all of my site images including homepage and page become blurry and stretched on mobile and tablet devices while they look good on desktop. The images are clear previously so I’m not sure if it’s related to the updated version of WordPress version. I am confused as most of site visitors come from mobile device.

And an interesting thing that when I opened the image in new tab via mobile, the image can become clear when I reload the page.

How can I solve the problem? Million thanks!

The page I need help with: [log in to see the link]