From my experience you are doing one of two things wrong.
1) You are slightly pivoting (backhand english) instead of going to the TOI with a parallel cue movement. It's so slight with me you wouldn't be able to see it. This is because my stroke is very precise, and yours will be too one day, however, now you may need to go over further. Make SURE your tip is flat against the inside of the cue ball telling you visually that your pool cue is perfectly straight, not "slanted" due to an unintentional pivot.
2) You may be following through at the contact point like you used to. This will decrease the natural deflection and you will be erratic. This system allows you to FEEL the cue ball and CREATE the angles....it's not about visual "aiming", I don't aim at anything on the object ball, I'm just aware of it's presence once I'm down.
When I'm getting down on the shot I JUST look at the cue ball until I"m locked in and am confident that the cue tip is square and the CENTER of the tip is flat against the ball. I look at the object ball as I"m hitting the cue ball and follow it into the pocket with my eyes, I want to see what part of the pocket the object ball enters so I know to adjust or not on my next shot.
I treat all shots like they're the same, so if I undercut one, I immediately adjust to slightly over cut the next shot.
I hope this helps, if I saw you hit a couple balls I would know exactly how to work with you, maybe sometime soon I'll have the virtual ability to do this, until then work with these suggestions they'll help for sure.