Hi,

I see that one screenshot is missing at:
https://appstream.debian.org/sid/main/issues/meritous.html

screenshot-download-error
Error while downloading screenshot from 'http://asceai.net/meritous/scr/screen4_full.png': Failure when receiving data from the peer on handle 7F2E054A02D0
This might be a temporary server issue. 

It's been that way for weeks now, so I believe that while this is reported as a transient error, its effect are permanent.

Intuitively I would expect appstream-generator so mark the screenshot for retry for the next cron :)