Solution : https://service.sap.com/sap/support/notes/555212 (SAP Service marketplace login required)
Key words : 
rfc server groups maintenance, manually implemented settings, previously active values, rfc reason, values permanently, individual values, resource specification, 's_rzl_adm' '01' authorization, make temporary, terms rz12
Related Notes : 
       
| 761274 | Parallel processing of tasks in the monitor | 
| 675725 | Unnecessary BDocs in SRM (EBP) from queue CSA_MASS_BUPA |