There are so many factors that can change between the first and second meeting between two teams. Things like injuries, lineups, tempo, +/- settings, type of defense, type of offense, distribution, 3-point settings, fatigue, fouls, IQ, etc. Plus there is the RNG! Upsets are real and they should be included in HD.
I know some coaches will disagree with me but I swear I remember TK saying that upsets were built into the game. He said that there were XX% upsets in real life and that same factor was built into the engine. Upsets are real and should be included in HD. I have lost when I was a 54 point favorite. It happens.