Belgian candi syrup crystalizing?

[EkieEgan]

Not beating myself up here. I know what I made is totally usable. I will just have to heat the mason jar up in hot water to liquify, but I'm not sure what I did wrong. It took me almost an hour to make the syrup as I followed a pretty decent video on youtube, but I obviously missed something. After I had the color I wanted (I didn't go TOO dark the first time because I was afraid of burning it), I turned the heat off and added water until it was thinned down. However, the syrup mostly crystalized as it cooled in the jar. Advice??

Here is the video I used. Seemed solid to me. I used pickling lime as well.