@vannal
Thank you for clarifying about the grade and confirming that it wasn't in progress. I know in the past there were sometimes issues with grades loading over, but I thought that issue was fully resolved. When I tested in my own course, I did see grades updating with multiple attempts, but there may be some other issue going on. The only time I got a different score was when I had something other than "Highest" set for the score.
Since you said you already confirmed it is set to "Highest", I would recommend contacting the Canvas admin/tech support at your school and/or Canvas Support with this issue so they can investigate it further. They would have more direct access to be able to work through additional troubleshooting with you on this.