Can't move or rotate viewport left or right

I’m not sure what I did, but suddenly I can’t use half of the viewport camera movement functions. If I left click and hold, I can still move forward and backward, but I can’t turn left or right. If I right click and drag, nothing happens at all. If I hold both mouse buttons down and drag, the view moves up/down and left/right as expected.

Any ideas about what might have happened? I’m only getting this behavior in one project.

I ended up doing a clean reinstall of Unreal Engine, which solved my issue.