Ultimately if we are struggling with consistency and cannot see why, we are FOR SURE doing something different from one day to the next – and just need to identify what that is.
Also, remember that the snooker balls will be in different positions from one day to the other so even if we are exactly the same in our execution, on table results can be hugely different from one day to another.
It is up to you to self diagnose whether it is cueing, aiming, or concentration that is causing the fluctuations. This is the reason for drills that demand precision (eg potting blacks / pinks / long blues off the spot and seeing how many times out of ten you can follow the cue ball into the same pocket), as they bring into awareness the micro mistakes we make which in turn will prompt us to self prescribe the micro solutions that we need to apply.
Sometimes, we will also have no clue whatsoever what our issue is – so get ready to accept that you won’t know around 25% of the time why you missed, or what you should do to play the previous shot better.
You can also try going in to the club and just having fun in some frames (maybe even on your own) where you have no pre shot routine, no post shot routine and play the first shot that comes into your head and in the way that you want. For example playing lots of side, or power, or playing a very difficult pot when you have an easy one available, playing the thinnest cuts you can see, setting the balls up again after five minutes… Maybe that will help you blow off some steam – as will taking a week off from the game from time to time.
Often, it is simply the expectation that we should play well which can handicap us from playing with freedom. What I used to find helpful in your situation was just getting back to staying down on the shot a bit longer than normal and committing ONLY to watching the ball to the pocket with 100% concentration – that would be my ONLY target for the shot and if I did it with 90% or above concentration then the shot was successful. This would get me back to the PROCESS of playing the shot and help me to remember that, actually, WATCHING THE BALL is more important than POTTING THE BALL – because without the former, we cannot do the latter!