Solution : https://service.sap.com/sap/support/notes/1034729 (SAP Service marketplace login required)
Key words :
$gantt-data[guid=$key]/bar_data/start_date, $gantt-data[guid=$key]/, takes significantly longer, remove character string, replace line<xsl, <bar_data/start_date, xslt transformation dpr_ui_gantt_xslt, $gantt-data, --graph data -->, $gantt-tree
Related Notes :
| 1031198 | Gantt: Performance |
| 929969 | cProjects 4.0 - Performance notes |