Solution : https://service.sap.com/sap/support/notes/1234971 (SAP Service marketplace login required)
Key words :
multiline container element, parforeach accesses automatically, container element, runtime automatically, workflow definition, object values, index access, longer compatible, &table[&_wf_parforeach_index&], system converts
Related Notes :
| 1083317 | Change to the ParForEach expression syntax |
| 1068627 | Composite note about workflow upgrade |