iʼve taken a look at this (mostly to see how ap works anyway, i donʼt understand it much), and it seems to be an issue primarily(?) on your side.
curl -H 'Accept: application/activity+json' schmaker.eu/objects/c83e3896-1…
gives both images in source.content and contentMap.cs, but only one in content and the other as attachment.
on the other hand, schmaker.eu/objects/c83e3896-1… has the pictures only in source.content and both are as attachments.
(i suspect the hashtag after the pictures, but idk.)