So, late to the party here but I too have experienced this on numerous occasions. It seems to be that when "displaying" waypoints, it consumed too much resources (I have the RC2) and it causes it to crash. The same when editing. Basically, if you can see the map with waypoints on it, and the number of waypoints are over 100, it is going to crash.
What I do to fly a mission with loads of waypoints is to change the view screen to have the main view as the camera view and then the Picture-in-picture showing the pitch/roll view, rather than the map. I can then call up the waypoint mission and fly the route happily(ish).
Also, if I want to edit, I pit the main screen to the map and then zoom in on the map so the umber of expected waypoints is really limited and then edit the waypoint mission. It will only show a very small subset of the flight but allows editing. You can still move the map around, as long as the number of visible waypoints is kept small.
These are not great workarounds, but at least they appear to work for me.