Missing a lot (relatively simple shots mainly, difficult ones seem to generate enough focus to take them down), and confidence is in the crapper. Negative self-talk is hard to banish (because... look at the simple run out you just blew [times 10]). Making 80% of the balls in a match but finding enough small ways to screw up that I lose the match. And on and on. This has been an issue for weeks now.
So, lack of focus, concentration, and confidence, and now it's affecting motivation as well. How do you get back on track?
First thing, you may have a little unrealistic expectations. Miss a shot and set it up ten times and you may be eight or nine out of ten. The same shot when you get one try during a game you may be only six or seven out of ten.
When I miss a shot I shouldn't, my reaction is "damn, that was stupid!" Followed immediately by "That ain't my norm." Now I have dealt with the miss, forget about it.
Getting shape while missing the pocket isn't getting half the shot right, the shot was misplanned from the jump! Other than speed errors, it is impossible to make half a shot perfectly as you describe unless the error was before you ever got down on the shot. I usually put more thought and effort into position because that is usually the harder part of the shot. Once down, I am usually going to pocket the ball and get shape, or miss both pocket and position. Rare for me to make half a shot and a real annoyance, means piss poor planning on my part.
The mental game never costs you a miss. It may set you up for flaws in your physical game but it is these flaws that cause the misses. A fine but necessary distinction because it means there are multiple problems that need fixing. On the mechanics side, I would study the table then bend over and bring the cue back slowly, smooth transition or slight pause depending on your preference, a gradual gathering of force going forward. One stroke then stop at the end of your followthrough and consider where your tip is at and why. If it seems to be the result of something during the approach or during tip contact it needs addressing. Not an issue if it is the result of something happening after the tip and cue ball have parted company. Shoot almost entire practice sessions like this until your game straightens out.
Your business but if it was me and I had a session with an instructor of JJ's ability, I would break the session down something like this: Five or ten minutes on session planning. Not over thirty minutes on fundamentals. The rest of the session on what you want to get from the session.
I am sure Jeremy can fix your basics but so can a lot of other people including yourself. I wouldn't "waste" a session with a world class player working on grade school issues.
Good Luck!
Hu