I managed to duo (just barely) a Kartana raid, and then noticed that it proved extraordinarily hard to catch, despite throwing curveballs with Golden Razz Berries. I didn’t even manage to catch it at all before I ran out of balls. I also noticed that for some reason I’d been given the plain old Premier Balls (like for most bosses) rather than the Beast Balls I got after my successful Pheromosa raid.
I wonder if that’s why I couldn’t catch Kartana—it easily escapes any ball that isn’t a Beast Ball? But if that’s the case, why didn’t Niantic give me Beast Balls this time?
As an aside, this particular Kartana was running Air Slash + Aerial Ace, which is why it was so hard to beat—Mega Zard and most of the usual counters take neutral damage from both moves, whereas they’d doubly resist Razor Leaf + Leaf Blade or X-Scissor. Kartana raids are especially subject to the luck of the draw in this regard.