I'd say it could be either or both.
You might start by using a heavier bell if you have one, as it can be self-correcting.
That said, the flipping up, plus the more up/down pattern I see (rather than more forward/back) indicates there's a little issue with your form as well.
To me, it looks like your force is being projected at about a 45-degree angle or steeper. So, it looks more upward than forward. Remember that you're projecting the bell forward, like you're "throwing" it for distance rather than height.
One visualization I use is that of the force being like a rubber band, like a slingshot. It throws the kettlebell forward, then throws it backward in the same path. Imagine a Y-shaped tree, and you've made it into a giant slingshot. Now imagine actually using it to fling a large rock at your enemy. Think about the path of the slingshot's pocket. It shoots forward (forward/slightly upward) throwing the rock, then snaps back in roughly the same path (backward/slightly downward).
Because the force is at a shallow angle, the kettlebell stays roughly in line with the arms (both in the forward-most and backward-most positions), so it doesn't flip up in either position. Not sure if that's helpful since it's hard to describe in text.
By a shallow angle, I'm thinking in terms of around 20 degrees, with the crotch being the horizontal plane. The force travels in that 20-degree line, forward is above the horizontal plane, backward is below the horizontal plane. Again, this is just a visualization of the force - not really the exact path of the kettlebell.
Man, I'm not sure if any of that makes any sense at all in text, but I know what I mean and it's been a helpful visualization for me.
And duh - forgot this earlier - doing towel swings can give you the same idea in a practical hands-on way.