'15 instantaneous fuel consumption pegged at 100mpg for over 6 miles

Greetings! I've had a used certified 2015 Prius with ~50K miles for 6 weeks. It has behaved as I would expect until yesterday. For fun on my commute, I reset the trip meter when I left the house because the first 4 miles of my commute are downhill (200m drop in all). I got 100mpg on the instantaneous meter and 99.9mpg average fuel consumption for the 4.4 mile trip down to the freeway. That surprised me, but it is downhill and I was trying hard not to use gas, so I thought it was possible. But then I powered up to merge onto the freeway and the instantaneous meter didn't drop. It didn't drop from 100mpg until somewhere between miles 10 and 11 on the trip despite travel at ~65mph throughout. Nor did the average fuel consumption readout on the trip drop from 99.9 until just after the instantaneous fuel consumption meter started behaving in a way I was used to (it dropped below 100 at first but was still running very high for the freeway for a few minutes). So to my thinking, the car was not actually calculating any fuel consumption for a little over 10 miles.

Alarmed, I called my local dealership and asked to speak to the repair department. I was told that this was normal for the first 10 miles of a trip, that the instantaneous meter would stay at 100mpg and then start calculating after the first 10 miles of a trip. Seemed fishy to me as I hadn't noticed that ever before.

I tested that assertion on a couple of short drives today and did not find that to be true. I reset the trip both before starting and also just after starting a drive. Both the instantaneous and average fuel consumption behaved normally.

Should I worry about this? Should I pursue it? Many thanks.

 

Thank you! Yes, so far it's only happened once.

Perhaps I shouldn't worry about it until it happens again, lol.

 

Thanks for the feedback! My friends affectionately call me "detail-oriented." But I notice that I'm not alone here in that regard, so I knew it would be the right crowd to ask.