@jfercalderon I'm having the same problem. Here's the detail in my situation: It only occurs when Opera is Fullscreen mode (well who doesn't use Opera in Fullscreen mode?), whenever I move the mouse pointer to the top of the screen, the top bar iOs menu appears (the bar is hidden in Fullscreen mode on my Mac), and when the bar goes back hidden, Opera's current window is shifted up, anyone with this problem can notice the little white bar at the bottom of Opera's current window, hence the mouse shifted down.
My only solutions atm: Try switching between tabs, it worked before, I'm not sure about the latest version of Opera.
or simply close and reopen the current tab which has the problem, no need to quit Opera.
*note: the shifted mouse distance can expand by the number of times you move the pointer top the screen, which makes the shifted distance bigger.