One observation from my side, maybe it'll help:
Today I was flying from Oslo to Tenerife.
I loaded 41 t fuel, loaded the aircraft, and so on.
I noticed, that after about 1 hour inflight the FOB-Value on the REPORT-Page of the MCDU was wrong, about 8 t below the true value.
Also the EFOB value was negative (about -0.5).
All other values (especially on the FUEL PRED page) were correct and showed the right numbers, also the FOB on the ECAM was the right one.
So only the FOB-value on the REPORT Page and the EFOB values were wrong.
On my side, I don't have problems with too high fuel consumption values.
I've attached the data folder, maybe my observation helps!