My wife and I both have been vaping for 8+ years. I make our juice. I lung inhale and she is mouth to lung. About 2 weeks ago she started to cough only on exhale. She has all the same equipment and using the same 2 flavors- Kringles Curse and Cinnamon Chill. There has been no changes in formula or equipment. She uses Nautilus Aspire with their factory 1.8 ohm coils at 15 watts. Also she has a Kanger Tech Top Box Nano. She has been using both of these with the same brand of tank, at 15watts,with factory coils and has 3 of the Nautilus Aspire tanks. I use the Kringles Curse , but use mine in temperature control and have no trouble. I hope someone has a reason for the cough on exhale. I have triple checked everything and changed her coil, made new formula, and checked all settings on both mods.