Hi Antony,
I've flagged your post for attention of support/devs to investigate on.
Do you have a link to the race results for the race(s) where this problem was seen?
This was a recent race that also had the issue but only for one driver and only on the second pit stop.
As I was racing the fuel changed mid race and started reflecting the current fuel in the car not what I had chosen. as you change the fuel it would flick all over the place on laps then settle. then after 20 seconds or so revert to the incorrect very low fuel. I had to monitor it closely and put it in as i hit the pits. i put in 27l I think but actually 30 was added.
This issue has caused me 2 races to have lost position and points.