Just thought I’d let everyone know that dropping the 1Zpresso, even a short fall onto a forgiving floor, can indeed cause the burr to seize, to the extent that disassembly will not unseize it. The burr would not drop out, even with the top but unbolted. 1zpresso then directed me to use a plastic hammer on the top bolt (where the handle fastens), with the grinder sitting on a folded towel. A rubber mallet will not work. As I did not have a plastic hammer head, I used a standard hammer onto a towel placed on the top nut. A few sharp taps and voila, the burr dropped out and I was then able to reassemble and recalibrate. All good.
Try to not unscrew the top grind setting cylinder, as reassembly of that is a pain. And they don’t like you to do that, I suppose due to the risk of thread stripping, misalignment or lubricant loss. But I may at some point carefully unscrew it to very lightly lubricate it.
I did email both 1ZPresso and my retailer for direction and permission, before I tried the hammer approach, even though I had read about it online. I did not wish to void the warranty.
Lesson learned: This is not as robust a grinder as it appears to be. Take care and don’t drop it. Mine had just rolled off the counter. I now treat it with kid gloves. I keep it in its case and will use that case for travel. Perhaps that’s over cautious, but once bitten, twice shy.