We see this situation from time to time in Canvas gradebooks. What it means is that at some point, the assignment already existed in your course, and then you imported a second copy, perhaps not even realizing it. That results in the duplication of assignment entries. If both are published and have due dates, both will populate into your gradebook view.
There is no easy way to integrate two sets of grades despite them being for the same actual assignment/quiz item. There is a way to resolve this but it's very messy
and tedious.
To resolve it, you'll want to delete one of the sets of assignments.
*However, I must urge caution in that procedure. You already saw that you have the situation where some of your students have submitted to one of the assignments but not the other. And vice versa. For example: Johnny might have turned in the first version and not the second. Suzie might have turned in the second version and not the first. And there may be some students will have done both but might have performed better on one than the other.
If you were to delete one column before cross-referencing, one set of turned-in work would be lost permanently.
You'll want to align all the duplicated assignments side by side by selecting View, Arrange By, then Assignment Name A-Z
This will alphabetize your grade list by name and then allow you to see any duplications.
From there, you'll need to decide which version you'll keep and which you'll delete. I would choose the column that is most full of submissions to keep. Then, copy all the grades from the column to delete over to the column to keep. That way, the keep column represents every single assignment turned in.
Once you complete that reconciling/transferring, let's check one other place. Highlight and copy the name of the assignment in question. Then click the Assignments Tab.
Paste the name of the assignment you're searching for into the search grid (shown in green). This will identify exactly where each copy of the assignment resides.
At this stage, I would rename one of them by clicking the three vertical dots next to the assignment name, select Edit, and then adding the word COPY to the name of the file.
Now you know, for certain, that this is the one that needs to be deleted.
Go back to your Gradebook view, make sure that is the one that has all grades copied out of it and into the other keep column. And make sure the column data matches.
In this example below, there are students who submitted twice but received 2 different scores.
Decide what to do with that. In most cases, give them the benefit of the doubt and keep the higher score.
Then go back to the Assignment Tab view, find both assignments again (like you did before) and delete the COPY.
If this sounds tedious, I'm afraid it is. Hopefully, you don't have too many instances where you've copied assignments that were already in your course.
The key is to be methodical in how you go through the above process.