Solution : https://service.sap.com/sap/support/notes/359907 (SAP Service marketplace login required)
Key words : 
number range object rf_beleg, symptom fi serializes, attached program corrections, open fi process '00001170', support package level 28, document number gaps, fi document number, external document numbers, company code belongs, number object
Related Notes : 
       
| 612211 | FI document number ranges bufferng for ERS parallel procssng | 
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| 399207 | Number ranges: STOPPED NUM error; avoiding buffers | 
| 363901 | Country-specific buffering RV_BELEG/number assignment in SD | 
| 333649 | Collective note, performance in Real Estate | 
| 315202 | Error in NUMBER_GET_NEXT | 
| 23835 | Buffering RV_BELEG / Number assignment in SD |