I must've missed something. Why use a mold release with container candles? You said they had been turning out fine until the last 6 batches. Are you using the same bottle of FO or has it changed? Buying FO on eBay is risky IMO, been there, done that. If you want a quality candle, you need quality ingredients. You can get pretty good deals from reputable suppliers if you look around. I don't know about your situation, especially if it's a mottle you're getting, but think if anything has changed between the good ones and the not so desirable batches. Is it the same batch of wax? Even the heat and humidity can cause problems.