Fuel mpg computer stuck at 30.1

[2013fordFiestauser]

Hello when I first had bought my 2013 Ford Fiesta SE the fuel computer screen was reading 38 to 42 mpg every day I were to drive it now for just the last 6 months it is stuck at 30.1 and does not move at all but when I reset it it shows automatically 42 mpg but then it trickles down to 30.1 again and is stuck there when I first used it after I had bought it the mpg fuel computer always stayed at 39 to 42 mpg now it does not for whatever mystery reason can someone help me figure this out ? I mean I do believe I am still receiving my e9 to 42 mpg but I would like my computer to show me this as well. Thanks.

 

[LionsTooth]

May have to do a CPU reset by disconnecting the battery for a few minutes.