Every time when a folder is selected to publish all assets within it, just three assets are published and not other assets. Steps to reproduce the issue: 1-Select a folder in DAM which contains four or more images.
2-Click on manage publication and then publish it.
As per internal JIRA of: #ASSETS-7803 - DMS7 - Upon Activation Settings.
It's working as designed. Folder publish to AEM publishes only the empty folder. The anamoly observed with three assets is because those three must have been used in folder thumbnail.
So moving forward, activate assets individually.