Did you print it with any supports? I can’t tell based on the angle, but when you have a problem in back of the model, the first thing that comes to mind would be the seams (which you identified). Cura slices models such that the seams are located on the back face. If you don’t have any supports and the layer sags, it could produce what I believe I’m looking at. Have you printed any calibration models to make sure everything is suppose to do what it’s suppose to?

Something like this:
https://www.thingiverse.com/thing:2656594