3729094 - Application error when try to add custom parent-child association MDF object as an Onboarding custom task

Create custom parent-child association MDF object and would like to add it as an Onboarding custom task.

However, face application error when try to open template editor in Manage custom tasks

SAP SuccessFactors Onboarding

custom mdf object, parent-child object, custom task,  , KBA , LOD-SF-OBX-NHA , New Hire Activities (activities, tasks, buddy, equipment) , Problem