Solution : https://service.sap.com/sap/support/notes/755342 (SAP Service marketplace login required)
Key words : 
command      alter system flush shared_pool, select      _optim_peek_user_binds = falsein init<sid>, execution path performance _optim_peek_user_binds reason, notice incorrect execution plans, terms bind variable peeking, prerequisites bind variable peeking, deactivate bind variable peeking, older sap kernel releases, oracle c-interface version 8, bind variable peeking
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