This may be related to a setting in Setyl which ensures that the Department, Location and Legal Entity of an Asset always reflects the Department, Location and Legal Entity of the Person to which that Asset is assigned.
You can change this setting in Settings > Company Settings > "Automation" along the top tab and under the title "Auto Assign Departments, Locations & Legal Entities" and then tick which fields you want to automatically update.
If the above setting is enabled and a Person is not a member of a Department, Location or Legal Entity then any Assets assigned to that Person will be updated to remove any Department, Location and Legal Entity which might be added to such Assets.
To fix this, simply ensure that the Person’s Department, Location and Legal Entity are populated.