Thumbnail failed to load on the channel

Is your AWS permissions set to public (read access / everyone)?

Yes, we did set AWS public access. Following is one video, my JSON file passed the feed requirement, I can even see thumbnail on my preview, just don't show live, is My JSON ok?
{
"id": "kn2F625BC0",
"title": "Our House For The Weekend",
"content": {
"dateAdded": "2017-09-13T08:08:31+0000",
"duration": 3480,
"videos": [{
"url": "http://d3hzdb1r6xb159.cloudfront.net/kn2f625bc0-our_house_for_the_weekend_main.mp4",
"quality": "HD",
"videoType": "MP4"
}],
"captions": [{
"url": "http://d3hzdb1r6xb159.cloudfront.net/kn2f625bc0-our_house_for_the_weekend-en.srt",
"language": "en",
"captionType": "CLOSED_CAPTION"
}]
},
"genres": ["romance", "comedy"],
"tags": ["comedy"],
"thumbnail": "http://d3hzdb1r6xb159.cloudfront.net/kn2f625bc0-our_house_for_the_weekend-800x450.jpg",
"releaseDate": "2017-09-01",
"shortDescription": "While house sitting for their in-laws, a married couples relationship is put to the test, when they lose the family cat. This freewheeling faux-doc is a hilarious look at sex, love and marriage and house sitting. Starring real life married filmmakers."
}, 

"donp88" wrote:
Is your AWS permissions set to public (read access / everyone)?

Yes, we did set AWS public access. Following is one video, my JSON file passed the feed requirement, I can even see thumbnail on my preview, just don't show live, is My JSON ok?
{
"id": "kn2F625BC0",
"title": "Our House For The Weekend",
"content": {
"dateAdded": "2017-09-13T08:08:31+0000",
"duration": 3480,
"videos": [{
"url": "http://d3hzdb1r6xb159.cloudfront.net/kn2f625bc0-our_house_for_the_weekend_main.mp4",
"quality": "HD",
"videoType": "MP4",
"captions": [{
"url": "http://d3hzdb1r6xb159.cloudfront.net/kn2f625bc0-our_house_for_the_weekend-en.srt",
"language": "en",
"captionType": "CLOSED_CAPTION"
},
"genres": ["romance", "comedy"],
"tags": ["comedy"],
"thumbnail": "http://d3hzdb1r6xb159.cloudfront.net/kn2f625bc0-our_house_for_the_weekend-800x450.jpg",
"releaseDate": "2017-09-01",
"shortDescription": "While house sitting for their in-laws, a married couples relationship is put to the test, when they lose the family cat. This freewheeling faux-doc is a hilarious look at sex, love and marriage and house sitting. Starring real life married filmmakers."
}, 

Does it still play the video on the channel?  Are you getting any errors on the feed section?

There is no error shown on the feed. I can see the thumbnail on my preview in my Roku developer account, but it just doesn't shown on the Roku channel, so Roku cannot publish the videos because of it. Thanks!

CsR - If you send me your json file, I can validate it through the software (Json Feed Manager) I've written to create and manage json feeds.  If there's a problem, the software will complain.

Is each image 800x450, &/or 16:9? 

Otherwise I would think it's a public/private setting of sorts. Could you try hosting your thumbnail images elsewhere? Although I guess these are quick thumbnail grabs from AWS & downloading each would be time consuming.

Did you update your Roku device after making some changes on your feed?