Solution : https://service.sap.com/sap/support/notes/99699 (SAP Service marketplace login required)
Key words : 
code page input/output minimum size, code page conversion tables, rsts/ccc/cache07 reason, output code page, 6a  input            ca, 6x     input            ca, output log displays, rsts/ccc/cache07, bytesrsts/ccc/cache07, cache         1134              input            ca
Related Notes : 
       
| 1345121 | Profile Parameters which should not be set in Unicode | 
| 1078824 | Code page converter writes zero-bytes / damaged box chars. | 
| 790099 | R/3 Parameter Settings for Unicode conversion | 
| 70965 | Char. set conversion buffer "CCC" seems too small | 
| 5470 | Syslog E14: Reorganized Buffer RSCPCCC ... |