After completing Kahl missions for months now, collecting all of the passwords to open the cache in the prison break mission gives me the most trouble. This mission is divided into two parts, with the second one requiring you to ride a gunship to the second half of the level. Unfortunately, if you happen to miss a password in the first part of the level, there's no way to backtrack, which makes this objective incompletable unless you restart the level. If you only have one or two codes before you get to the gunship in the first half of the level, it really makes you consider if you should backtrack to see if you missed any passwords or if you should just go ahead and hope that you don't miss anything.
For this, I have a few suggestions. If you get near a password, a waypoint marker could appear that shows you where the password is in order to mitigate the risk of missing a password. Another idea that I found from this thread, is for the mission to tell you beforehand how many passwords have spawned on each half of the level, in order to save some time from backtracking:
Aside from the topic above, I haven't seen too many recent posts complaining about this issue, and I hope this brings some awareness to how annoying it is to miss and look for these passwords.