I just checked on the KPA I started yesterday. . .it’s brewing fine (as viewed from the outside of the bucket – there’s lots of krauesen that I can see when I shine a light through), but no bubbles are evident in the air lock (which is quite firmly in place). So, I’m pretty certain that the bucket lid isn’t entirely airtight, and a little carbon dioxide is escaping somewhere around the edges. Fortunately, this seems to be a pretty small deal in the grand scheme of home brewing, so I’m still not going to worry about it.