I looked through the troubleshooting guide and could not find a solution (that looks like the problem)...
For some reason in my big prints, the lower layers print right, but as the print gets taller and taller, it's almost like my machine forgets what the model is supposed to look like.
That back section is supposed to be solid legs with a support to hold up the cross beam.
This is not the only print that has done this.
Small models print fine.