There has been quite a bit of speculation regarding the formation of this scent/taste in kava in general (not just this kava). I first experienced 10 years ago in the Cook Islands. Locally sold Fijian kava smelled like a mix between plastic, kerosene and some solvent.
Dr JD Baker suggests that the smell is caused by mould. If I remember correctly, he suggested that this smell is due to styrne that can, under certain conditions (excessive moisture content, etc), be formed by the mold flora occuring in excess in kava. Mike tests his kava for mould, so even if this is the case, it must be due to the presence of a specific type of mould, not overall load as his kava doesn't have excessivem mould content.
Others (including Mike) have suggested this is due to the use of industrial plastic packaging in Fiji and packing warm/hot kava into these bags, which results in the kava absorbing some of the compounds from the plastic packaging.
EDIT: it was
@Kapmcrunk who provided this info.
"this can sometimes happen when they're pounding the kava and transfer it to the bags too quick without letting it cool down" (
http://kavaforums.com/forum/threads/re-kwk-loa-waka-bad-smell-issue-resolved.15125/page-2)
in any case, as
@Kapmcrunk suggested, just get in touch with them and they will surely provide and answer and make things right.