I have experienced countless issues with setting up missons with my anafi as well. I finally got it to work only yo have another issue.
I found that if you saved the mission before trying to fly it, it seems to work. Open the app, choose which flight grid you want, choose the parameters of the mission and elevation, then click the floppy disk icon to save it. Go back to the home screen and into project list, then try to fly the mission and it works. I found when I did not save it first that it would sit on the check list screen and never work.
Like I said I ran into a bigger issue when flying a mission. I started a mission and everything worked fine. My drone got to the end point and just hovered. A notification popped up on my phone and said drone hovering, resume mission or take over manually. I hit resume mission and the time it took me to do that and look up, my drone was gone No where in sight and I was unable to find it. I have flown many practice flights to make sure the app worked and the one time I take it into the field for commercial use, this happens. I have read and heard of many similar “fly off” incidents.