I've been trying to get the "Explorer" achievement to unlock the Silver Tank for the campaign editor, but as far as I know, I think it's unachievable, here's why I think so:

I found and completed all of the secret missions (I think) except for 47, and I think secret mission 47 is unreachable.

I know where the pressure plate is in mission 46 (Face Your Fears), but when I go to where the pressure plate is, I don't hear the 'click'.

Is this a glitch, or is there some rework of the secret missions going on?

So I got to where you get the Electro tank, got to the checkpoint, and decided to get off the game for the day. Then I came back and for some reason, my progress wasn't saved. So I got it again and left the game without Alt4ing or whatnot, and used the the exit button in the main menu to leave the game. It still didn't save the progress I made, so am I doing something wrong or is there a bug that needs to be fixed?

Help

Tank

Plz respond