2010 Prius "Consv. MPG" Data Frozen

I believe the CONS. abbreviation stands for consumption. I've never seen mine stick like that. I do the same thing, reset Trip A every time I refill. The mpg readout will indicate 99.9 for a little while, but it surely should have decreased to a reasonable value in 10 miles. In those 10 miles did the ICE run? If it was all electric for those 10 miles the 99.9 mpg might have persisted. Switch the display to Trip B and see if the value is different. I use Trip B for my tire rotation meter, so it accumulates an mpg value based on a number of tank refills. It might also be a 12 V battery problem. When the 12 V starts going south, the electrical gremlins come out. It's worth a check. Beyond that, maybe a code if a sensor is out of whack. There is a fuel flow measurement being made somewhere to provide the mpg value.