gr4v1ty,
Thank you for confirming you have Messages in iCloud set up.
Take a look over this article: Get help with Messages in iCloud - Apple Support, which shares troubleshooting steps for missing images/attachments, and messages not updating across devices. See if this can help get both devices synced up again.
You may also want to consider freeing up more storage in iCloud, or upgrading your iCloud storage, as 100 MB may not be enough storage required to sync over the other attachments. This information is found within the same article shared above, under the section titled, 'If you exceed your iCloud storage limit'. You'll find links in this section to help you with this further, as well.
Regards.