Some objects and particles are culled at certain angles when they should not be. I tested this with other performance mods at the time, namely Embeddium, Canary, Starlight, and ModernFix. Objects and particles at certain angles seem to bug out. For example, minecarts with chests will cull when looked at from certain angles.

That's not Entityculling. Either the minecart+chest is gone or neither, not just the minecart. Particles are not touched at all by EntityCulling. The angle is also not used at all, so rotating the camera has 0 impact on what the mod culls or doesn't cull.

I see. Sorry then, I'll go take a further look to see what's going on.

You can bind a debug key in the hotkeys to turn on/off the mod during gameplay, that should show that it stays hidden. In both screenshots there seem also to be weirdly not rendered chunks?

The rendered chunks is due to the fact that my chunk loading speed was kind of slow and I flew to a high location

I'm taking your word that the mod itself isn't causing the issue but I believe it's another performance mod that is messing with entityculling because disabling it through key binds fixed the issue.

EDIT: I think the issue is being caused by some weird interaction between this mod and either Entity Model Features or Entity Texture Features but it's been fixed