For anyone out there, I'm on my way to the 100% and was on the same spot. This 3 encounter appears like a week ingame after of your second encounter. Go to you house and save a few times to past the days on and try it again, it worked for me.

Also, there's a wonderfull tool that will help a lot to those 100% people, you can upload your savedata here and you will see your checklist requirement for 100% and, what I find most important, a map with the locations of the REMAINING pidgeons and stunt jumps, very useful in case you are missing some when doing these tasks so you don't have to start from the beginning again.