Yesterday I met a similar situation, I thought that the result of updating iTunes connect on August 8, 2016, was a red exclamation of all localized languages without the information of others. If you meet this situation from August 8, 2016, this may be the case.
I contacted Apple support and finally introduced a new version as I filled in screenshots for all sizes.
while you can upload a screenshot of the maximum size and "reuse" it for a smaller size on the "Media Manager" page.
Vin.w.
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