Solution : https://service.sap.com/sap/support/notes/848055 (SAP Service marketplace login required)
Key words : 
sapbwnews bw sp13 netweaver'04 stack 13, 10 content            import support package 22, 0b            import support package 28, entries disappear reason, no_read_stats solution bw 3, 50            import support package 13, 1 content support package 22, 0b support package 28, terms olap cache, cache statistics values
Related Notes : 
       
| 1107434 | OLAP cache consultation: Long wait times due to locks | 
| 989793 | Deactivating the read statistics for OLAP Cache BI 7.0 | 
| 856226 | Logging mechanism to analyse Cache related problems | 
| 783254 | SAPBWNews BW Support Package 13 NW'04 Stack 13 RIN | 
| 783252 | SAPBWNews BW 3.1 Content Support Package 22 | 
| 783170 | SAPBWNews BW 3.0B Support Package 28 |