I am glad I found at least one person with the same problem...I am already doubting my own sanity.

I could speculate now what's going on, but I suspect a design flaw...that maybe it's not flooding as most people vape with high VG - and it's more flooding with people who vape with 60/40 or 50/50. (Of course, this is just a guess).

My hunch would then that the oval airholes are simply too big, and TBH compared my KFL with tiny juice channels takes everything I throw on it without any issues. Because of that I cannot understand why these holes must be so big. As one single person (!!) on ecig forum pointed out

that you're relying on the surface tension of the wick/juice at the wicking holes to prevent the juice from the tank from flooding into the deck. This makes it more sensitive and susceptible to temperature changes. I learned this from leaving it in my hot car for a very short time. Juice expanding in the tank flooded into the deck/coil area

I also noted that it may draw ok at first, but that setting it down for some time then also triggers flooding. SOMETHING is off with that device.

The solution with just plugging a lot of cotton in there may work (haven't tried tho), but it seems like a solution which doesn't really address the underlying problem (eg. that the chamber is too open and that only the cotton stops the juice to get in)

Anyway..I now stuffed more layers of cotton into my existing build. Another thinkable solution would be to use a mesh or similar (pipe screen?) or some other (heat-resistant) way to reduce juice flow somehow.

(I can almost certainly exclude a defect with my device, oring etc. all seem alright, it's tight when I close the airflow hole and suck. Machining is not "super great" but is ok, can also exclude.

Also: Your method with simply more cotton (basically really stuffing the chamber) seems to work for now.