Cloudformation intrinsic function Fn::Sub mapping

You are giving the Fn::Sub function 3 arguments:

1. The String
2. Mapping for Lambda2
3. Mapping for Lambda1

Move both Mappings to a single list item and it will work (I also used the "dot-notation" for !GetAtt for simplicity but that's optional).

  DefinitionString: !Sub 
    - |-
      {
         [...]
      }
    - Lambda2: !GetAtt LambdaSubmitJob.Arn
      Lambda1: !GetAtt LambdaJobStatusPoll.Arn

Hope that helps :)