I looked over a couple of your photo's. I would see if you can put the wings down and see if it would lift the middle of your mower up some, so you can clear the ridge with the middle tires. If your wings are set to "float", meaning follow the contour of the land my plan won't work. But if you could plumb the wings to hold the position you put them in this might work.
Another idea might be, put the wings down and lift the middle tires up with a $80 high lift jack and see if the tractor can snatch the mower to clear the ridge of the hole.
No way you could have seen that hole but always go slow on new ground because the faster you go, the deeper in the s%$# you go. Good Luck.