The round summary screen after a match is almost always buggy, especially if I’ve completed one or two missions. Let’s say I have missions A, B, and C. If I complete 1 or 2, the performance tab will often have mission C in two boxes with no mention of missions A or B. Both boxes for mission C might even have different amounts of XP listed to complete.
Looks to me like when you start a match you references for three mission objects are saved, but something bungles those references up. I suspect that completing a mission changes its address, but neglects to update the references.
I should have taken a screenshot, but let’s say the performance tab has slots 1, 2, and 3 and you have missions A, B, and C. If you complete mission A, you would expect to see either missions A and B in slots 1 and 2 or slots 2 and 3. What happens is you might get mission B in slot 1 and repeated in slot 2. It’s pretty clear when the error occurs.