I could swear I read that was caused by overheating the wax. Let me look. I think I bookmarked it.
Edit: I wasn’t able to find article about soy candle flubs & their causes. However found the following article. Maybe candle was poured in too hot? Article mentions allowing wax to cool to 95F before pouring per online recommendations.
Sometimes this can happen if the colorant isn't combined thoroughly enough. Does it look like it's shimmery? Some colourants, for example micas, don't actually get incorporated into the wax, just dispersed.