I have the exact same issue going on, I just don't get why it all of the sudden struggles to wick efficiently. I have tried the .25, .5, and the NI200 coils all with the same issues. I tried a long low and slow break in as well as a hot and heavy just go for it break in with the same results. I've recently noticed that I can get the bubbles to float up if I rotate the tank around, it almost like they are getting trapped and blocking juice flow. I cannot find anything wrong with the machining or Orings but there has to be some sort of vacuum issue but I don't have any leaks either.
I've actually emailed Uwell about this cause I'm at wits end with solutions. Right now I'm using my last fresh .25 coil testing|
what a few have recommended in regards to a break in period where you vape a couple tanks worth at around 40 watts. So far it's been ok, but I haven't exactly reached the point where I typically get dry burn.
If I hear back from Uwell or this break in thing works I'll let know but at the present time I'm thinking of just biting the bullet, trashing them and getting the tvf4...m