"Gary
if u changed your push level for the last lap (High push level) then u can run out of fuel on final lap if u r running tight on fuel.
This.
The drivers decision to pit the lap earlier is based on his current push setting for that lap. So if you were on 1/5 for the second to last lap, they judge their fuel for the final lap based on 1/5 push level. So if you change to 5/5, there's a good chance to will run short if you were already marginal.