Regarding the thumbnail sizes issue, I contact Photon support and they reply me as below. Any suggestion?
I can see what you mean. The problem is being caused by this setting in your site’s stylesheet (CSS) :
.featured-content img: width: auto
Photon delivers thumbnails in 2 sizes now, 100×100 and also 200×200 for HiDPI/Retina displays. Your posts with the large thumbnail displaying, have a larger featured image specified, so Photon is making both thumbnail sizes available and the “auto” width setting in your CSS is grabbing the larger size.
You’ll need to remove that setting for your CSS, or make sure it doesn’t apply to these thumbnails on your main page. If you are not familiar with CSS, you could pass along this information to your theme’s designer for their assistance.
Happiness Engineer | Jetpack.me | WordPress.com