How does (campaign) enemy ACS strain ACTUALLY work in AC6?

doing my second full clear of the game and overall haveing a great time, but once again I'm confused on ACS strain. Why can I do like 90% strain to an enemy, and it just... disappears, in an instant? is there a special move you can do to reduce it that isnt explicitly stated , or is the AI just cheating? The strange feeling of 'unfairness' has always annoyed me (like how they seem to recover from stagger FAR faster than you do). I can see it from just a balance thing to make them stronger against the player (fair enough), but I just want to know if im missing something.