FQI and their accuracy is some serious black magic. To confirm you actually had a leak and not just misbehaving readings a couple of additional steps may be necessary. Did you take any?
To illustrate I used to fly particular MSN which seem to show a constant leak from whatever had been the FOB down to about 4000 kgs, at which point the fuel magically re-appeared. After one cautious en-route diversion as a result of this, and .... plus .... with ...., it turned out that all was within the FQI specification. Nicely explained in the old (discontinued) blue FCOM bulletin: FQI Accuracy.