Unfortunately, the game is also still a bit buggy in regards to triggering (or failing to trigger) certain missions. Hopefully, it's just a case of you forgetting a mission or something, and not a game breaking bug :(
Did you by any chance max out Franklin's shooting skill by going to an ammunation with a gun range? I had the same problem with that heist, but I didn't realize at first that I had to do that as well.
You don't have to have max skill on him to start it. I did do some range challenges, but I never even tried to come close to maxing his skill and the mission started fine for me. Now there may be some amount you need of course, I believe that heist has a message from Trevor "suggesting" that Franklin go get better at shooting... but I totally ignored as I already worked on some shooting skill before. Think I was around 60, maybe 80.
PC: You don't want to know... >_> <_< 3DS FC: 2363-5768-5754