Refilling the e-liquid in an improper way.
Orings, refilling pad glass, and cotton is not in good condition.
Vaping setting is improper.
Sitting for a long time after refilling.
Make sure orings, seal and glass are all good and everything is tight. Use e-liquid to lubricate o rings during installation.
When you use RBA coil, make sure you stuff the cotton in there really good.
You can also take it all apart and screwed the coil into the base nice and then screwed the top bit on making sure it's all tight and make sure the seals are perfect
Make sure coil bottom capes are clamped all the way down and make sure air holes are closed when refilling.
Make sure the atomizer has been cooled down while you refill the tank because the liquid flows faster when the atomizer is hot.
Please finish the refilling as soon as possible.
Please try to vape at an appropriately high wattage which is recommended on the coil during vaping. It may encounter the leaking issue if the liquid on the coil hasn't been atomized on time with low wattage.
Besides, please close all the airholes when you do not use it.