Interesting. I have my bottle opened since years ago and no crystals ever. Pretty humid environment here too. I have had tiny containers that dried out totally and it was more like a smooth plastic surface, no crystals either. I have purchased a new bottle just because the old one has a gum-like consistency now, but it still closed and unused. Some added water keeps the old one like new.
Their explanation looks a little poor for me, too. And if you have never encountered the problem before I would be inclined for the changed formula issue. I’ll keep an eye on my new bottle!