Check your gang management at a crib and see if you have the Decker Cars and Decker Gang Style (rewards you also get with that Stronghold). Sounds like you encountered a serious glitch.
If you have access to Co-op, maybe you can find someone before that mission and doing it will fix something, but that's grasping at straws on my part.
Other things to try: - Clear your cache and restart the game, but do not download the update (play offline) and see if the crib triggers (I doubt this will work, but what's the harm in trying) - See if you can get into the crib via the helipad (since it uses elevators to get inside and these are often enable by a code flag, I'm skeptical this will work, but again, no harm in trying - Update: this won't work if the power plant wasn't replaced with the stronghold, Decker version has neither helipad nor garage areas) - Do the same with the garage and see if you can even retrieve cars from it (Update: this won't work if the power plant wasn't replaced with the stronghold, Decker version has neither helipad nor garage areas) - Join someone's game with the crib and see if entering it can do anything to change your situation - Have someone join your game and see if they can enter the stronghold (both as a character that has and has not unlocked it)
Definitely report this and as much detail as you can to Volition so a fix may appear in the next Update (kinda wish they'd rollback the Dec 12 one).