What do you mean by "exploded view"? Let me know what you mean so that I can show you.
The waist, and all 4 limb joints in combine mode has the 'lock' buttons. However you don't have to use them when connecting the knees (but they are necessary to disconnect).
The shoulders need you to be pushing the button as you connect the arms and because they are tiny, this can be very tricky as there is two of them for each shoulder that need to be pushed simultaneously. Once done, the arm joint will go all the way in and very smoothly. When you release the button, it will be fixed very solidly and move easily through the ratchet joint and able to maintain poses.
When it comes to Mixmaster, the robot mode waist (the connector from 'cab' to 'barrel trailer' in vehicle mode) needs to be pushed in through a similar button as the arms. You can only do this when the cab is in 'foot mode'. You will notice that it will shorten and level with the other leg.
The waist connect though 'clips' that only hook up properly if you align them while pushing little buttons that open up the 'hooks' connectors that clamp on the waist. When you release the buttons, the waist clamps into the torso.