Tuffer,
You really haven't given us enough information to provide a definitive answer. It could be one of several things.
I'm going to assume from your question that the student did better than 74 on the final.
The old gradebook had an option to treat missing grades as 0. That didn't actually make them 0, it just showed you what would happen if the grades were 0. That was confusing and Canvas moved it to just the individual view. With the new gradebook, missing grades are not automatically set to 0 unless you have a missing assignment policy in place. Check the gradebook and see if there are 0's there.
The use and weighting of the assignment groups can also affect the grades. Again, I don't know how you have things set up, so I can only show possibilities.
Let's say that you have an exam category worth 60% of the grade and it has a midterm an a final. On the midterm, the student got a 80. On the other 40% of the grade, they had a 68.
Their grade going into the final would have been 0.40*67 + 0.60*80 = 74.
On the final they got an 76. You might think their grade would go up because they did better than the 74.
What is happening is that their average for the exams is no (80+76)/2 = 78 (assuming you weight them equally).
That makes their new grade 0.40*67 + 0.60*78 = 72.8 or about 73%
The point here is that with weighted grades, you shouldn't be looking at the final compared to the class score, but the final compared to the previous score in that assignment group.
If you have drop rules, then that can affect things because grades don't get dropped until there are enough grades to drop them and still leave at least one item in the assignment group.
There could be other things like extra credit or some assignment groups that didn't have any grades in them so far. Those aren't as likely as the final relative to the other items in the assignment group.
Hopefully one of those will be the solution.
