Does it happen when you are chain-vaping? It may be as simple as your tank overheating. However, since it seems to be isolated to certain liquids and if they are high VG, Bombastinator is correct that a few drops of distilled water in the tank should fix it, both by increasing wicking, but also water has a lower boiling point than VG definitely and PG (possibly, I can't remember the exact order). I've used Max VG in my tanks and have thinned, up to 10% DW (really the highest you can go without a watery anemic vape). It did make a significant difference both with temps in the tank and coil life improving. So that may be something to try. You may want to look at which liquids are working best in the tank and if they are all higher PG, it may be as simple as keeping your ratios the same.
If you are chainvaping though, with a high VG liquid, that could be the source of your problems. Most vapers have at least one setup as a backup, and if you have a backup that works for you, you may want to pull it out during "high vaping" times, so you aren't overheating your tank.
It is true, I have heard of some smok coils having wicking issues and needing judicious pokes with a pin here and there to improve juice flow through the tanks, but as a non-smok user, I'm not entirely sure which ones and would probably try the above remedies first, since it doesn't sound like you are getting "dry" or "burnt" hits which is what I would expect, just that your tank is overheating. You may want to open your airflow more too, if you can, that should cause more air to circulate within the tank and may lower temps somewhat.
Best of luck,
Anna
