I remember having this issue often and it usually affected only one of my quad windows. I never found a solution but I have tried a couple of things and I haven't yet experienced this come back.
So you could try and click on "Orthographic" at the top left of the window and choose "Left" or "Right" just to reset the orientation of the window.
You might also have an overload of detail on the screen so the camera does not have enough resources to render the entire model and bone system. Try to disable turbosmooth temporarily (if you have any) to see if this helps to at least troubleshoot if this was the issue.
If you are working in 3DsMax 2017, try installing service packs (there are 3) which might fix this issue. If you are working in another version, try looking for available service packs.
Finally if nothing works, try working in a different window (I have resorted to this previously and the error seemed to not occur in a different window)
Good luck!
