Mine has stopped calculating mileage too, but only in the profile of one of our cars. Last successful entry was 2 December.
Your vehicle's situation is a little different.
The fill-up on December 16 you marked your Odometer reading as 605.
I believe you meant you traveled 605 miles so you Odometer should read 91510 based on your Odo marked on Dec 2. Simply edit this fill-up and your data will be sorted correctly. Because of the Odo being marked as 605, it bumped that last fill-up all the way to your first one which can be seen here: http://www.fuelly.com/driver/peteplus/cerato/log/page/2
Hope this helps both of you. Any further questions, just let me know. I'll monitor this thread for the next couple of days or you can reach me via Fuelly Mail or the Help Desk.