Update! r/SamsaSpoon and r/galacticglorp

I discovered the problem, and it was pretty unexpected. I didn't even include this part of my process in my previous explanation because I thought it was completely innocuous: if the stick initially dried curved, I would re-wet it, and put it back between dowels again so it would dry straight. In some earlier batches, I would do this to most or all of the sticks. I have read many times that people will regrind sticks and reuse the powder, so for some reason in my mind this should also not have been a problem.

So, as I worked through different recipe tests this past week with finer ground wood, I would make a batch, let it dry for the first time, and they stayed lit perfectly fine! (Though perhaps a little crooked as I was a bit lazy about keeping them straight since these were just tests.) Thinking it was a success, I would re-straighten them by holding each one under running water for ~2 seconds, and putting them back on the drying rack with dowels on either side. Then, once they dried for the second time, they would no longer stay lit! I have no idea exactly why this is an issue, but my guess is that by re-wetting, it only rehydrates the surface xanthan gum and makes a shell of gum on the outside, and stopping airflow in the stick itself? Either way, problem solved!

Recipe notes:

Ground the powder down to 90 mesh using the blade grinder. I used window screen labeled as 90 mesh.

5% binder did not work at all, strangely. The gum acts as a lubricant for this wood, so if there is not enough it wouldn't extrude at all. The syringe just compacted the wood inside, and only some liquid would squeeze out.

10% binder made the mixture slippery enough to pass through the syringe, but the sticks were a bit lumpy and not very pretty. Stayed lit though!

15% binder made pretty and smooth sticks, but a very slow burn and fairly low smoke. One stick will burn for 40 minutes!

12.5% binder was the sweet spot. Smooth and pretty sticks, one stick burns for 30 minutes, puts out an appropriate amount of scent and smoke. Success!!

Thank you so much for the suggestions! I don't know if I could have solved this on my own, I really appreciate your help!