The middle fuel-up (10.25 gallons) is marked as partial fuel-up (ie. you didn't top off the tanks). That means it cannot calculate the gallons consumed since the previous full tank. Then the 15.37 gallon fuel-up would be the first full tank after so no MPG will show until the next complete fuel-up.
Do you remember if the 10.25 was indeed a partial fuel or did you maybe check that on accident?
i had this same problem with a vehicle i just purchased and added to fuelly. had it not been for this thread, i would have made a new thread wondering what was wrong. indeed all 3 of the fill ups on my new explorer were checked as "partial fill ups". i did not check this option when filling. the fill ups were added via iphone 5 on the app.
i edited each fill up and now everything looks fine. we shall see if my next fill up automatically uses the "partial fill up" option