my fuel consumption went up after using Ron95Xtra

previously using Shell 95 then Petronas 95 my mileage is around 11.xxkm/L to even 12.xxkm/L but now with the new Xtra, my mileage is 9.xxkm/L

i always keep a record of my fuel usage using an app on my iphone so it cant be wrong. Either my car suddenly minum more or Xtra drinks more.

Now Im switching back to Shell for a month to see whats my results