Hello There,
After successfully uploading data into AAM, backend jobs take 48hours to process this data and get it rendered onto UI which is the same case for data being available for targeting purposes.
It is always advised that we should perform ID sync first before uploading data into AAM.
In above mentioned scenario, as you performed the ID sync after data upload, these 3 users will not be account for trait/segment population in AAM due to which you are not seeing desired experience for given users.
To get things sorted, please follow below steps:
1. Perform ID sync for all the users
2. Upload data.
3. Wait for 48hours for this data to be available for targeting.
4. Now try to access your website for any of the user.
The highlighted statement "If the data provider is configured to use Profile Merge Rules for cross-device targeting, the data available for targeting shortly after an ID sync identifies to the matching Audience Manager visitor ID." represents the scenario where same user is coming from multiple devices in that situation an ID sync from a new device will help in syncing the user from rest of its linked device but in situations where no device is present for a user then the statement does not work in the same way.
If you would like us to investigate more on this, please raise a ticket with us via amsupport@adobe.com so that we can investigate this scenario in further detail by checking for the 3 specific users and their ID sync.