In 4x4 the right front wheel and left front wheel rotate at different speeds. And sometimes not at all depending on the situation. However, if you are in “Differential Lock” and the right front wheel isn’t locked, then the issue could be within your differential itself. Or perhaps the linkage to the 2wd/4wd/differential lock needs to be adjusted. Might not be fully engaging differential lock if that’s the case. That or you might have a busted cv joint on that right axle. But if you did you’d definitely hear it. And welcome to the Forum.