The reasons were the same as well regarding the blades and control algorithms/systems. If they haven't improved things for the charlie model, then they'll likely experience the same issues and failure rate.
It's a little more complicated than that. One had an issue with the landing system. It was flying just fine, but the autoland datalink hand-off wasn't working. They tried and tried, but couldn't get it to sync, so they did a control ditch. That one was the one strapped to the side of the ship for a bit. I know of at least another one where they think it encountered icing (or some sort of moisture accumulation issue). There was no way to know it was flying in the clouds at the time (it was enroute with no sensor active), and had a loss of control.
The earlier deployments (mid-2000's) had some control/software issues, but the system matured (relatively) by the ought-teens...or whatever we're calling that time period now.