Solution : https://service.sap.com/sap/support/notes/365093 (SAP Service marketplace login required)
Key words : 
additional key words database inconsistency, intercepts extremely rare error situations, correct inexplicably occurring gaps, number range object rf_beleg, issue error messages, symptom actual gaps, program corrections attached, document number gap, number range, document number
Related Notes : 
       
| 428391 | Inexplicable document number gaps in FI (II) | 
| 175047 | Causes for FI document number gaps (RF_BELEG) |