I think some enemies can master strike you. I dont think I was ever master striked when I played through the story though.

The enemies, or more precisely the game can do many things which automatically land hits but so far I'd say your having a smooth playthrough. The thing about this game is that you ultimately have to get up close and I mean really close and do not let your enemy have any room.

On my first playthrough I could kick when ever I want and that really helped a lot. Now though I cant kick unless its a fist fight and I dont know why but it helps much less.

What probably happens is that some extra oponent got one in from behind and then your locked opponent had their way with you.

Or the single enemy got out of range somehow for your attack and then hit you and you fell into something, maybe a bush or maybe a fence of some kind, and so you were waiting for that knockback effect to wear off and that single enemy had their way with you.

Or maybe they parried and then hit you with a combo while your computer stuttered and didnt load the icon, allowing them to have their way with you.

Or maybe yet still what happened was you stumbled over a small uncocher bit of terrain or up some bushes and they had their way with you.

In any case the developers left grease on the floor after making the fight system and you probably slipped on it. Stay away from bushes in this game.