I am having this same problem whether I use 1.3.74, 2.3.70, 1.3.68, 1.3.62, 1.3.59 and 1.3.52
I draw a polygon of about 5km x 5km. I select Auto WP => Survey (Grid) You can see the rest of the settings form the images below. It looks like I have a nice zig zag flight plan. When I click Accept then I get a silly flight plan that seems to ignore every second waypoint and looks like the second image below.
What changed, why, and how do I fix it ?
I have tried deleting the Mission Planner folder in c:\ProgramData.
I have tried deleting the program for version 1.3.74 from C:\Program Files and re extracting the zip file for it.
I have tried Alt F then selecting Param Gen