Candi sugar problems around 130°C — what happened?

Today I was brewing a candi sugar. Recipe I use is simple: unrefined beet sugar, white sugar (for cost saving), a pinch of dry malt extract for Millard reactions, and water just to dissolve it all. Then heat to 120 — 130°C, keep at this range for an hour or so, heat to 150°C, pour on baking paper and let it cool.

Previous time result was like a brown glass. Smooth. And making it was straightforward, it stayed liquid all the time, from start to finish.

This time when I reached around 130°C, sugar suddenly started to solidify, formed thick mass and big solid chunks. I added hot water to keep it from burning, tried to keep it closer to 120°C, but this happened again. Result has less rich taste and is not so transparent. And of course brighter, because I kept it, on average, at lower temperature, but colour I can easily work around in finished product.

What might be the reason for this difference? Using more % of unrefined cane sugar could cause this? Original Belgian candi is 100% unrefined, so I expected it to be better. Or maybe going too fast with heating? I used pot better suited for induction this time. Or anything else I should think of?