Unable to create a custom subobject instance on the Modern UX, if no other instance exists and both the Name and ID fields are auto-numbered

Document ID : KB000125667
Last Modified Date : 10/04/2019
Show Technical Document Details
Issue:
STEPS TO REPRODUCE 
1.    On the Classic UI, create a subobject of the Project object called Sub1 
2.    On the attributes tab, auto-number the ID field 
3.    On the Classic UI, create a subobject of the Project object called Sub2
4.    On the attributes tab, auto-number the ID and Name fields   
5.    On the Modern UX, go to Administration > Blueprints > Create a new Blueprint
6.    On the Modules tab, edit the Blueprint and add both Sub1 and Sub2 subobjects
7.    Publish the Blueprint 
8.    Associate a project template to the Blueprint 
9.    On the Modern UX > Projects, create a new project based on the template associated to our Blueprint
10.    Go to the Sub1 tab and click on the Plus sign
11.    A new subobject instance is created
12.    Go to the Sub2 tab and click on the Plus sign
11.    A new subobject instance is created

Expected results: A new subobject instance is created 
Actual results: No subobject instance is created 
Cause:
This is caused by DE47132
Resolution:
This is fixed in 15.6.1.


WORKAROUND: 
1. Do not auto-number both Name and ID fields.
2. Create a first subobject instance on the project on the Classic UI. Subsequent instances can be created without a problem
Additional Information:
A similar case scenario:
Following the steps to reproduce, if on the subobject of the Project object called Sub2, if the ID is autonumbered, the Name is not, but it does have a default value, the result is the same: No subobject instance is created if no other instance exist.
This specific case is fixed in 15.6