I've seen some pictures of people's e-liquids where some look like ink they are that dark!
But my main concern, as it is a key ingredient, is the safety of inahing PG and VG (esp. long term). They are not toxic. However, PG can be irritating and VG is very slow to evaporate (how well or not it is absorbed by the lungs is unknown). So potentially both could lead to chronic bronchitis (inflammation) which is experienced as wheezing/difficulty breathing and extra mucous needing to be coughed up (and which is extra sticky).
If you get these symptoms, try not to deep lung inhale. If it persists, stop vaping for 1-2 weeks and see if things improve. Then try again, with minmal lung inhalation. If these symptoms return again then you would have to try vaping less (look into WTA and snus). There will be some people who just can't do the inhalation of PG or VG without this result. While PG is far more likely to cause classic intolerance, imo VG is more likely to cause the sticky mucous issue. A no-glycol e-liquid would be welcome.
The danger of ignoring chronic bronchitis is increased chance of a serious lung infection, such as pneumonia. The older you are the more likely to get this proble, and the more careful you need to be about it.
This issue could present as fast as a day or two. It's not easy to differentiate this from smoking withdrawal (detox) and getting a cold, so don't be too quick to jump to conclusions, but cut down or stop vaping in the meantime.