it's most likely my aim because for a couple of years my vision centre was offline (too far to my right) , so i was perceiving slight right english as center ball. so when i wanted to put on slight left english many times i was actually hitting center ball with no spin.
now that i have moved my vision centre online i have fixed the issue but i think that years of offline alignment/wrong perception have made it more difficult for me to get used to stroking with left english, especially if i want to put on a big amount of it, so i think what sometimes happens is when i want to put on more than 1 tip of left english, sometimes i'm not actually aiming on that spot, i'm aiming with less left english than i think and then i put on more spin on the final stroke.
sometimes flaws are hard to get rid of especially if you've been doing it for years, so you need a lot of practice to completely remove them from your game.