Project is not getting saved from project server 2013 custom PDP (Error AssignmentCannotEditSummaryTask)

I am Working with Project Server 2013 on-premise. We are using custom PDPs to edit project information. Project gets created successfully using project creation PDP. User opens the project information page to edit the project and while saving the project after making some changes, Project isn't getting properly saved and in Queue, it gives the below error-

While going through the error details, It is clear that it is not supporting summary level resource assignments in the schedule. and i have tested it, if i remove the resource assignment from summary tasks then it solves the issue.

So my question is that why it's giving an error while saving from custom PDP due to schedule. Although, I am not a developer but If it is customization issue, so knowing something i can help my Dev team to avoid this issue.

Error Details - 

Datasets:

• ProjectDataSet
  • Table Assignment
    • Row: ASSN_UID='c856368a-fdcb-e511-899f-0a34dcdb4dc4' PROJ_UID='5feabcd4-c9fe-e411-9406-0050569842e6'
      • Error AssignmentCannotEditSummaryTask (135) - column
    • Row: ASSN_UID='e8b83aaf-fecb-e511-899f-0a34dcdb4f84' PROJ_UID='5feabcd4-c9fe-e411-9406-0050569842e6'
      • Error AssignmentCannotEditSummaryTask (135) - column
    • Row: ASSN_UID='62595dba-fecb-e511-899f-0a34dcdb4f84' PROJ_UID='5feabcd4-c9fe-e411-9406-0050569842e6'
      • Error AssignmentCannotEditSummaryTask (135) - column
    • Row: ASSN_UID='fa7c61c1-fecb-e511-899f-0a34dcdb4f84' PROJ_UID='5feabcd4-c9fe-e411-9406-0050569842e6'
      • Error AssignmentCannotEditSummaryTask (135) - column
    • Row: ASSN_UID='13163b4f-ffcb-e511-899f-0a34dcdb4f84' PROJ_UID='5feabcd4-c9fe-e411-9406-0050569842e6'
      • Error AssignmentCannotEditSummaryTask (135) - column
    • Row: ASSN_UID='b4cd66a3-ffcb-e511-899f-0a34dcdb4f84' PROJ_UID='5feabcd4-c9fe-e411-9406-0050569842e6'
      • Error AssignmentCannotEditSummaryTask (135) - column
    • Row: ASSN_UID='ade758fc-00cc-e511-899f-0a34dcdb4f84' PROJ_UID='5feabcd4-c9fe-e411-9406-0050569842e6'
      • Error AssignmentCannotEditSummaryTask (135) - column
    • Row: ASSN_UID='03ef9fc4-02cc-e511-899f-0c84dcdb4f84' PROJ_UID='5feabcd4-c9fe-e411-9406-0050569842e6'
      • Error AssignmentCannotEditSummaryTask (135) - column
    • Row: ASSN_UID='eec02d09-03cc-e511-899f-0c84dcdb4f84' PROJ_UID='5feabcd4-c9fe-e411-9406-0050569842e6'
      • Error AssignmentCannotEditSummaryTask (135) - column
    • Row: ASSN_UID='efc02d09-03cc-e511-899f-0a34dcdb4f84' PROJ_UID='5feabcd4-c9fe-e411-9406-0050569842e6'
      • Error AssignmentCannotEditSummaryTask (135) - column
    • Row: ASSN_UID='109db912-03cc-e511-899f-0a34dcdb4f84' PROJ_UID='5feabcd4-c9fe-e411-9406-0050569842e6'
      • Error AssignmentCannotEditSummaryTask (135) - column
    • Row: ASSN_UID='e4b1836c-62dc-e511-af72-f0921c5c2db3' PROJ_UID='5feabcd4-c9fe-e411-9406-0050569842e6'
      • Error AssignmentCannotEditSummaryTask (135) - column
    • Row: ASSN_UID='1cf83ca3-62dc-e511-af72-fc421c5c2db3' PROJ_UID='5feabcd4-c9fe-e411-9406-0050569842e6'
      • Error AssignmentCannotEditSummaryTask (135) - column
    • Row: ASSN_UID='55b4c8ad-63dc-e511-af72-fc421c5c2db3' PROJ_UID='5feabcd4-c9fe-e411-9406-0050569842e6'
      • Error AssignmentCannotEditSummaryTask (135) - column
    • Row: ASSN_UID='a50e9a6a-64dc-e511-af72-fc421c5c2db3' PROJ_UID='5feabcd4-c9fe-e411-9406-0050569842e6'
      • Error AssignmentCannotEditSummaryTask (135) - column
    • Row: ASSN_UID='d9d0b782-65dc-e511-af72-fc421c5c2db3' PROJ_UID='5feabcd4-c9fe-e411-9406-0050569842e6'
      • Error AssignmentCannotEditSummaryTask (135) - column
    • Row: ASSN_UID='48e86222-66dc-e511-af72-fc421c5c2db3' PROJ_UID='5feabcd4-c9fe-e411-9406-0050569842e6'
      • Error AssignmentCannotEditSummaryTask (135) - column

General

• Queue:
  • GeneralQueueJobFailed (26000) - ProjectUpdate.ProjectUpdateMessage. Details: id='26000' name='GeneralQueueJobFailed' uid='e2357b08-38e1-e511-430a-005056980065' JobUID='2d2a4c432-15f7-4be9-b520-24e61c371b26' ComputerName='ID' GroupType='ProjectUpdate' MessageType='ProjectUpdateMessage' MessageId='2' Stage='' CorrelationUID='ID'. For more details, check the ULS logs on machineID for entries with JobUID.