I finally worked out repeatability
I'm using a Flair neo with a bottomless portafilter and a 1zpresso J-Ultra. From what I have read this combo should be capable of some really top tier coffee when used correctly. Until the last couple weeks it's been wildly hit or miss. Occasionally the coffee is great, usually it's meh and I have not been able to figure out the difference between the two. Back-to-back shots would be great then aweful. After years with the flair and maybe 6 months with the J-Ultra I think I have finally dialed in the most important part of the process... Me.
I saw a post a while back where someone was upset that their hand grinding speed had a pretty significant impact on their grind size, or at least how it flowed. I've been trying to stay consistent but obviously a couple beans would catch at once and there's a decent amount of hitching and stopping. I had a thought a couple weeks ago and started turning the crank differently. Instead of just spinning the handle so the beans made all the resistance I started pulling out away from the grinder as it goes around. Not crazy hard but enough that at least as much force is pulling the crank away from the grinder as is turning the handle and grinding the beans. Now my handle is barely slowing down when several beans catch at once and it's not speeding up when the beans run out of get caught. It takes a bit more arm strength but results suddenly got way more consistent.
I have also been trying to get my blind shaker figured out. I assumed this was not a big deal and would just shake some then use the funnel to drop it down in the portafilter. Having weird inconsistent results here too! Grounds would be stuck in clumps all around the inside and it would be all lopsided when I dropped it into the Portafilter. After running across some simple little process videos I noticed that people were not shaking thair shaker anywhere near as hard or for as long as I was. I got gentler and tried to shake in the same ways and about the same amount of time every time. Much better now. Grounds are fluffier and clumps aren't getting stuck to the inside anymore. Maybe due to the funnel into the 40mm Portafilter but grounds would still usually be higher on one side than the other. I finally got my WDT back out and stirred the ground around in the portafilter just enough to level it nicely before some gentle taps and a tamp.
Now finally I have repeatability! I can dial a few clicks courser or finer and see those results in a slightly faster or slower shot. I can make no changes and get very nearly identical results back to back.
TLDR, even the little details make a big difference. Even if you think that part of the process doesnt really matter, it probably does.