I have the same issue. I've updated my iphone to the latest version 2.0.36 and I keep getting the same message under waypoints "corner radius invalid" I've tried changing angles, altitude, size, everything I can think of and nothing helps.
I've also tried creating a brand new flight plan and still get the same issue.
What do I need to do? This is very frustrating with the 99.00 per month I'm paying.