Solution : https://service.sap.com/sap/support/notes/1622015 (SAP Service marketplace login required)
Key words : 
function module enh_delete_enh_from_cross repeatedly invokes unnecessary tree-building activities, long running conflicting accesses, renaming enhancement implementations, global enhancement overview, database table dwtree, terms enhancement framework, prerequisites program error, support package suitable, unnecessary, enh_build_tree_in_background reason
Related Notes : 
       
| 1558728 | Performance improvement of after import method | 
| 1420290 | Performance when importing EHP/SP for enhancements | 
| 1062559 | XPRA_UPG phase hangs due to database table DWTREE |