Hello @Prabin Paudel - I'm responding on behalf of Anurag so please tag me if you have further queries on this matter.
It seems that you are attempting to reference users by their
displayName (of AAD attribute) for work item assignment but Azure Boards doc states that the
System.AssignedTo is a reference type that's pre-defined by the system: https://learn.microsoft.com/en-us/azure/devops/boards/work-items/work-item-fields?view=azure-devops#system-and-predefined-fields
We also find here that the
System.AssignedTo is of String data type and corresponds to entries in AAD user accounts, and synchronization occurs between Azure Boards and AAD for person-name and other fields. This is where, I believe, you may be running into issues where the LA connector is expecting a value that complies with that of reference field, but instead, it's receiving a value from
displayName (which let you define custom formatting for the full name of the users as: Firstname Lastname (CAT)).
For more info on Reference names and why they are needed in Portability of definitions across integrations, please review: Field reference names and portability
The reason why you get the
displayName as expected with manual assignment is probably because the People picker tool in Azure Boards is automatically synchronizing fields from AAD behind the scenes.
I hope this helps understand what you have observed above, please tag me and let me know if you have more questions.