Achievement problem "Scar Zero"

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Played on the release using the manual, brought all 4 units including Scar Zero to the secret laboratory, reached chapter 6 at the moment where you need to defend for the last time, I go up to 2 units and nothing happens.
If someone also faced a similar problem and was able to get achievements, tell us how to "cure" it.
1. imgur.com/a/6sGILJ5
2. imgur.com/a/bNJH7Pt
3. imgur.com/a/3RFhKLj
4. imgur.com/a/2yuRXly

[Trivvy™]

There are two possibilities as to why an achievement hasn't fired.

1. Cheats / console commands were used at some point
2. Your connection to Steam may have been down at the time.

If you suspect it's number 2, you can reload your save to before the achievement should trigger, make sure your Steam connection is good, and then try to trigger it again to get the achievement.

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@Trivvy™
I do not use cheats, the game is so easy. The problem was solved by reinstalling the game on another hard drive, beforehand I made copies of the saves, as I approached Scar Zero, they immediately gave achievements.