There are some triggers on the map, when you cross them and alert the horde. Sometimes the special infected may spawn from front and go back to you, crossing that trigger and he will stupidly alert the horde. Can you please fix that?

This is more like one of those cases of a bug turned feature. Although it was intended to make these triggers behave like the vast majority of other triggers in Left 4 Dead several years ago, a lot of time has passed and some people found this 'bug' interesting and fun. It adds to the variety in the gameplay experience, but isn't too impactful/potentially run ending. This campaign is intended to be unforgiving, thus players should always be ready. It can even be used to the team's advantage to trigger the horde from a safer place. Furthermore, since there is nothing in the surroundings of the triggers justifying the alerting of a horde (no loud or major event) it's actually a bit more realistic for the specials to call it (by making a fuss or somehow rallying up the nearby commons) rather than the survivors by just passing there. So, this is currently viewed as a 'unique' experience from Labirinferno, along with some others.

Therefore, for now, this behaviour won't be changed, but thanks anyways for the participation. However, if a lot of people show discontent with this behaviour, it isn't ruled out that it would be changed.