I know exactly what the OP is talking about. It has happened on some, if not all, of my BM knives when new (710, 746, 940, and currently on my Custom Shop 550; I don't remember if I had this issue with my 520, 943, or 15030). After flipping open and closed a few hundred times from EDC'ing it goes away... at least in my experience.
This usually happens to me when I try to flick it with my thumb, it doesn't open all the way, and I "flick" it the rest of the way. It can also happen if I do the thumb-flick combined with a wrist-flick.
If I were to guess, I would guess that the AXIS barbell is seating slightly off-kilter when flicked in such a manner, and shoves the barbell into position unevenly. I believe that the design of the AXIS lock allows for the "barbell" to move further towards the blade over time, to maintain a strong lockup. However if it seats off kilter, it might allow a portion of the barbell to seat further in, causing a higher level of friction when disengaging the lock. I could be wrong.
I tend to believe that this is not a good thing, but all of my other BM's lost this issue over time. My newest Custom Shop 550 has this issue, but its new. Because of this, I try to limit my "wrist-flick" opening for when I am holding the lock open through the entire opening arc. This is also why I like the 3rd finger flick opening method. It works on smooth opening thumbstud knives too.