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All my steemit feed has posts without thumbnails like below screen capture.
I've noticed that, for instance under Trending Feed , we have UnBoxing My World Cup Tickets Paid for by Steem and it loads fine but thumbnail isn't loaded.
After some investigation, thumbnail looks to have a broken or improper link.
Whereas actual image link should be
After further investigation, I've noticed that https://cdn.steemitimages.com has been filtered by Domain name filter in our network i.e. any resources(like images) host in this site "https://cdn.steemitimages.com" will be blocked from accessing.
I've started this post as to report an issue but eventually found the reason why thumbnails are not loading myself. Hopefully, someone might find it useful.