I bet if you look more you'll see more cracks in the frame. I brace mine all the way from the body mount under the door to the very front taking out the front body mount I'll try to get some pics, I've went as far as the whole front bracing too plus inside the frame to the motor mount.
Yes, there are more crack on the back of that cross member. Nothing on the frame, yet.
Any pics you have would be great.