E.g. when I sneak, other players descend into the sneak animation, and when I harvest a block, other players' arms begin moving. This is not purely clientside as the other player who I was with when I noticed this commented on it as well. This is on a dedicated server where firstperson is only being used clientside. Probably a conflict with something.

List of mods:
mods.txt

You have 480 mods installed, what makes you think it's firstperson mod? Especially since this mod does nothing in regards to animations. I did have one report like that over on Not Enough Animations but without any way to reproduce it, there is nothing I could look into.

You have 480 mods installed, what makes you think it's firstperson mod? Especially since this mod does nothing in regards to animations. I did have one report like that over on Not Enough Animations but without any way to reproduce it, there is nothing I could look into.

Ah, sorry, I forgot to mention that the behavior stops when I use F6 to toggle the mod off.

I should also probably clarify that when I said that the other player noticed it, I mean that they noticed their limbs moving in sync to my actions, not the other way around. It seems like it's less a problem with animations and more like both of our models being synced to my player? Although that's a layman's guess.

Try again without NEA or going into F5. As I said, this mod doesnt have anything to do with limbs or sneaking.

Try again without NEA or going into F5. As I said, this mod doesnt have anything to do with limbs or sneaking.

Apologies for the delay, took me a bit to get the opportunity to test it again. You were correct and not enough animations seems to be the offending mod.

Try again without NEA or going into F5. As I said, this mod doesnt have anything to do with limbs or sneaking.

Apologies for the delay, took me a bit to get the opportunity to test it again. You were correct and not enough animations seems to be the offending mod.

Then the question is, what do you have installed to make nea break like this? Since this doesn't happen usually.

Ok, managed to find something: During the ladder animation the player gets set to not be visually crouching to not mess with the animation. But something would have to go terribly wrong for that to incorrectly trigger or be shared between players. Can you test if turning off the ladder animation fixes it?

That does appear to have fixed it thus far with ladder animations turned off for the both of us, although it's been somewhat inconsistent, so I'll keep an eye on it. Not sure if it's player by player but I tried testing it with a different person yesterday and couldn't get the issue to register at all regardless of what it was set to for both of us. This player did have the glitch, however and the ladder tweak appears to have worked.