Hello Ivan,
If you uploaded the user list a couple of hours ago and seeing the Populating status via UI then it is expected. It takes 6 to 12 hours for a list to be populated with members, so you'll most likely see an "In Progress" status (on the Google Ads UI) if you upload to an audience list more frequently than once every 12 hours. To know more about customer match considerations please refer
this guide.
If the problem persists please share the SOAP logs(
request and response) of the upload operation performed without redacting any data. You could refer
this guide to enable logging for Java client library, for other client libraries please refer
here. You could use reply privately to the author option while sharign the information requested.
Regards,
Sai Teja, AdWords API Team