I got that too with one i bought about 6 months ago. I had a pre-loved one which we had used a lot with no issues at all so I couldn't work out what it could be. In the end I wondered if it was something in the dye maybe?
Whatever it was, I strip washed the nappy using the dishwasher tablet method, gave it a few extra rinses and it has been fine since. And yes, the HL BB smell far far worse than any of our other night nappies