On Keyboard and mouse while moving the camera, the target changes

[Tao]

Its soooo annoying how to disable or fix this bug

[ExTremZ]

thats normal, just dont move the mouse.

[Imperator Ricardo]

It is not a bug, it is a mechanic that is supposed to help you switch lockon targets.
It is a bit finnicky on mouse and keyboard, since the game is designed with mainly controllers in mind, but the solution is to move the mouse as little as possible, or not at all as the previous poster stated.
Do so, and it will not happen, just let the Lock-on do the camera movement for you instead, or release the lock-on if you need to adjust the camera manually on certain attacks/bosses.