Thank you for your valuable feedback regarding the new API.
We are also able to observe the same issue of lookup values getting mixed up when added for the same task. We have logged this issue as TASKSNET-1786 for further investigation by our product team. We’ll update you once there is any further progress or a fix version available in this regard.
This issue has been fixed in the latest release of Aspose.Tasks for .NET 17.8. Please download and check it at your end.