Check the replay. Then monitor their health. Sometimes, seeing it again, and doing the math, will explain it. For example, you “blink”, or weren’t paying attention b/c of Macro, or microing something else, and they did end up taking enough damage because enough time passed.
For Miner Evacuation, note that there are Volatile Infested that do 40 damage apiece. So Artanis and Karax Zealots have (hp + shield) 100/50 and 150/50 respectively. 4 to 5 is enough to wipe them out in an instant. Even a few short of that is easy enough for remaining infested types to finish them off. Zealots are melee, so they tend to rush into a group of them, unless you micro them