Hi there,
Thanks for replying.
That's an interesting question. But, that comment on mobile IDs and cookie IDs present in one segment is in different context. Lets keep that one aside.
Consider that you have a rule based trait for online and onboarded trait for offline data. They are being used in a segment that is mapped to an ad platform.
First, AAM segment population will always have device IDs (AAM Cookie ID). So, thats a good thing because there are no two IDs present (CRM and Cookie) in the segment, and all of these IDs are deduplicated.
Second, if segment comprises of an onboarded trait linked to a cross device data source, then segment must be using a Profile Merge rule.
Profile merge rule that uses current device as device option will take into consideration historical devices as well in segment. So your total segment population will have all those devices that are not recently active. It could be possible that there are devices in segment that are older enough and never had an id sync with ad platform. As ID sync for that ad platform gets enabled when you get S2S destination created.
Another reason could be: Ad platforms have TTL for their own IDs. Like AAM cookie ID TTL is 180 days and Ad Platform ID TTL could be 30 days or lesser etc.
I would recommend to log a ticket with AAM support team for further investigation. You could also request them to send a Full Sync file to ad platform on a more frequent basis.
Thanks,
Varun Kalra