Level/Mission not registering as being complete

This problem can occur for two reasons:

Cheat codes. Developer mode gives access to functions beyond entering 'cheats' for the game. It is recommended that cheats are not used if this problem occurs

Skipping cut scenes. If the cut scenes (scenes when answering the phone etc..) have been skipped too quickly it can in certain circumstances prevent progression. Allow the cut scenes to play for a few moments before skipping