Try this: take a sledge hammer and knock (not too hard) the leaning pieces back in. More like a tap. Work your way through the leaning pieces gradually knocking them back into a more "upright" stance. This approach has helped me stay away from the dreaded restack.
(note - My stacks are on pallets, 40" wide - which is usually 2 rows with the middle filled with shorties/uglies)
Yeah I do this regular. My outter stack is inbetween two 6x6 posts. When the stack shrinks it starts to lean.
I trend to cut & stack in the summer. Am the only mug cutting when its +27C. 'Early bird' and all that.
Cool tractor BTW!