This I know. My Buddha's Hand syrup is just like your syrup. Almost completely crystals.
I can't figure out what happened. I have the opposite problem of crystals forming when I don't want them. I put some orange/ginger syrup into a jar just before Christmas and there were solid crystals from the outside of the jar to within an inch of the middle, with only a cone-shaped area that is still syrupy in the middle. As I needed syrup, I added a little water and gradually melted it in the microwave until I could pour all of it out of the jar.
I heated it a bit more, in a Pyrex measure, in the microwave and after pouring out what I needed for my recipe, left the Pyrex container sitting on the counter and when I came back to it, a couple of hours later, crystals had already begun to form around the edges. Anything containing sugar (without any corn syrup, honey or etc.) will try to crystallize as the water is expelled or evaporates.
What do you suggest I do? If any. If not, well, it has ceased to matter... Thanks