Other mistake: Miles, a 17 - or 18-year-old whose "grades were trash", may have been able to fix his motorcycle, but it seems highly unlikely that he would be able to fix (a few times) a highly advanced robotic dog like A-X-L. [A-X-L was able to self-correct certain things.].
Continuity mistake: A-X-L frequently varied in size. For example, sometimes its head looked massive compared to Miles, being about the size of Miles from his head to waist. Other times, A-X-L's head looked about twice the size of Miles' or Sara's head. A-X-L's body was sometimes about the same size of Miles' motorcycle but much larger other times. A-X-L looked much smaller when it was dragging Sam compared to when it was standing over Sam.