These things are so finicky. I can be vaping along innocently minding my own business and all of a sudden, gurgle and boom. Mouthful of juice.
I don't get it. I can refill a few times and all's great and then refill one and blammo. Leaking like banshee.
Love these things when they work but it's like black magic to keep them from betraying you.
I suspect you are a victim of stress cracks in the clear tube or barrel. You can check that by holding them horizontally under a strong light source and rotating them slowly. The cracks, if they are cracked, will show up very plainly. That can be cured with clear nail polish, or a colored nail polish if you like, or with clear tape. If there are any cracks what happens is that just a tiny amount of air can seep in through them which disturbs the pressure differential inside the CE3 causing everything from gurgling to outright leaking depending on how badly they are cracked.