Some armor stands are now culled too aggressively, see the 2 screenshots below.
I mainly noticed it with hunt traps in the Skyblock of Hypixel but it can probably happen with some other armor stands.

With Entity Culling 1.9.2:

With Entity Culling 1.9.1:

Thats... odd? There was a change, because armor stands didn't get culled when they should be on (which got noticed in the sky block housing area) 939b8bb Can you tell me how to get to that area so I can look at these? Or can you test binding the culling boxes keybind in 1.21.8

and show the result of that?

Worstcase I need to expand the culling boxes, assuming these are armorstand holding the trapdoor in their hands or having them on their head(?) in a way, that it goes over a block above the normal armorstand head 🤔.

I don't see anything when showing the culling boxes after binding the key.
And it's an item you place on the ground: a Huntrap, you can also see one on Galatea besides Dax.
I can also see this happening with with the Mana Flux Power Orb.
Oh more commonly you can see it with pets beside the players, they're sometimes disappearing while they are still on your screen.

I never played housing or skyblock, so getting the things is not an option for me 😅. And seems like I accidentally broke the debug boxes maybe for some versions. I have to do some testing, possible these markers have a stupid small hitbox or something, and that causes the failed culling.

You can at least test the last thing I found for Skyblock, just start a profile, do /hub, then you'll see pets floating beside other players.
I see it disappearing when it's on the bottom of the screen. I would guess the armorstand is below.
For the Mana Flux, I can put one down and you'll be able to see it!