The ball never goes where you want it to but it always goes where you put it
Could be stroke but my guess is you are not lining up the balls correctly to begin with. That is, by far, the shot I show people when they are working on their stroke and EVERY time I do it I tell them "the balls MUST be lined up perfectly straight EVERY time or none of it matters". They chuckle and say, yeah, I know. I set up the first one and show them, edges of ball line up, centers lined up with center of pocket. Then I proceed to shoot it and follow it in (not always

) then have them set it up. 99% of the time the balls are not lined up exactly spot on center of CB/center of OB/center of pocket.
The problem is, especially after playing as long as you have, you will automatically adjust for the difference - not realizing it.
I suggest you try putting the CB on the head spot and shoot down table to the center diamond and have the ball come back and hit your tip, this drill will help you notice any deficiencies in your stroke better than the other one as there are less things involved. When I get off track and stop focusing I have a tendency to put a little left on the ball, I use the spot drill to identify it.