Never believe the lying fuel computer!
Having said that, that’s a big difference, one would normally expect a 5% variation in my experience.
Could the last reset have been done on a downhill stretch at a steady speed? ?
Try a computer reset at the same time you next fill up.
2024 - BMW i4 Grand Coupe eDrive 35 Sport
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2017 - Audi Q3 TFSi Sport S-Tronic