I support an instructor who is experiencing something similar with a New Quiz that has a mix of auto-graded and manually graded questions.
The grade at the bottom of the New Quiz in Speedgrader was updated immediately with the manually graded questions, but the Gradebook item did not update immediately. The grade was eventually updated in the grade book after some time passed.
I've tested a mock-up New Quiz in my personal sandbox course and have been able to replicate the issue with two test accounts. I tested the quiz around 11:30 am and it didn't update immediately. I just checked the score now and it's updated at 1:50pm. For some reason the other test account is still behind on updating the score.
I've found past posts where Canvas claims this issue has been resolved, but the lag in updating the results is concerning and frustrating.