I'm also working on a map series. My map change does work from second to third. So what I did that could work for you is to use a Trigger_changelevel. Then within its properties type the name of the map that you want to change to and enter the name of the landmark on that next level.

I did this same thing in the second level but this time I made the info_landmark be named something different. (Not sure if it matters but it works) The trigger_changelevel can be triggered or it can be walked through.

So this is what I did for my first map:
I made the trigger_changelevel be:

(When "Next" is triggered the level will change)
NAME: Next
NEW MAP NAME: RX1_SubSpace
LANDMARK NAME: lm
CHANGE TARGET: Empty Field
DELAY BEFORE CHANGE TARGET: 0

Then in the map RX1_SubSapce the info_landmark is:

NAME: lm

In the second level I made the trigger_changelevel be:

NAME: No Name
NEW MAP NAME: RX1b_SubSpace
LANDMARK NAME: lm2
CHANGE TARGET: Empty Field
DELAY BEFORE CHANGE TARGET: 0

Then in the map RX1b_SubSpace the info_landmark is:

NAME: lm2
I hope this helps.

The change level sone can be reached only when you are holding the "crouch" button. What if this is the problem.