I believe the flat spot is caused by the case mouth being jammed against the mouth of the chamber/action on the way out - I believe this means the lever may not be retracted far enough to have the ejector kick the case out before the bolt moves forward when you lever it or the extractor may be holding onto the case until the lever moves the bolt forward enough to kick it off the edge of the chamber/action area. Either way, the brass should be reloadable.
Do you use both new and older brass for your loads? Does this happen with both? Does your ejector/bolt need lube???