This is a new one in Cubase 12 that didn’t occur in Cubase 11. When changing the time code of a session and selecting “Keep everything at it’s current time code”, the Video Player window displays the incorrect image after the change. Closing and reopening the player fixes this. The same is true for the Time Code window. The code doesn’t match until you close and open the window.
Cubase 12.0.30, Mac Pro, OS 10.14.6.