On every atomizer I had which lost taste and vapor I looked into the atomizer to find burnt material just under the bridge, at the peek. The area between the actual bridge mesh and metal bridge under it. I picked this material out with tweezers for the atty to never function again. It was a fiberglass type strand.
Ah ok, the wick.
I dissected he first 510 atty I had that died and pulled the wick out. It had turned dark brown in spots and I assumed it was burnt. But I went and washed everything after disassembly to use the parts... and the wick washed out to a clean white color.
So in my experience what's actually burning isn't the wick itself- its the juice that gets gunked up on the wick and won't wash out.
The end result is the same: nasty flavor. But its not as creepy as actual burning plastic which has been documented with the cartos.
That's my opinion anyway.