I think you found the reason by your own, external list behaviour.
With external list, the tracking log data are attached to only one contact, the same for all records, and usually it is contact iRecipientId #0 so not shown by Adobe Campaign. But it can be another contact, sometimes the first of the external list.
So with admin role, please display the contact id and the folder for this contact. And check if the normal user can accede to this user, frequently recipients folders are split/filtered by some rules such as departements, geographic entities, etc.
OK wkt, so probably something about privileges or local cache for this user.
Do you test on the same PC, switching from the normal user to admin user? Please may you check with normal user account, but by cleansing the AC local cache in the File menu ("Vider le cache local") then disconnect/close app and relaunch. If the same issue occurs, check the normal user his privileges carefully.