Unit Group - Pick each unit in (Command Center (Infestable) units in (Entire map) owned by player 4 matching Excluded: Missile, Dead, Hidden, with at most Any Amount) and do (Actions)
Unit - Add 1 Infested to (Picked unit) from player 4
Spotted the bug! Change "Picked player" to "Picked unit". At the moment you are adding the behavior to player, not unit.
I have already encountered issues with "matching conditions", it did not work at all, but I can't say which condition or what is the bug. Not sure if it was the same problem than you have, but you could try to select your units an other way to be sure.