Activision is aware of the freezes and lock-ups that are randomly occurring on Call of Duty: Black Ops II for both the PlayStation 3 and Nintendo Wii U.
In a statement on their support page, Activision states:
“A patch has been released to fix the lock-up/freeze issues affecting Call of Duty: Black Ops II online gameplay on PlayStation 3. However, we are aware that some customers are still experiencing PS3 lock-ups after installing the patch and we are doing everything we can to get to the bottom of it as quickly as possible.”
As for the Wii U version, Activision says that the lock-ups that occur when trying to load a saved game, may be happening due to not having a recent version of the game.
“Be sure to install all patches or title updates as they become available. Patches and updates provide significant improvements to games, such as increased security, or fixes for exploits or crashes that may occur.”