When in first person and not holding an item, the player's arms do not move when walking, punching or throwing out an item from the inventory. This is especially noticeable when shaders with shadows are enabled or when throwing out an item from the inventory when nothing is equipped in the main hand. (On 1.17.1 Fabric)

Ok then this is teeeeechnically a duplicate of tr7zw/FirstPersonModel#125 which teeeechnically should be here. Apparently while in first person the player model doesnt update correctly, causing the arms to behave this stiff. Will keep track of it here.

Oh didn't realize someone had already posted about it but yeah thanks!

Yea but I guess it technically is on the wrong mod. I thought that it's an issue with the firstperson paperdoll in combination with this mod, but since it seems to happen without the firstperson mod, visible through shaders, I guess the issue is fully on this mod.

Oh yeah that's true. Good luck with it though.

Wait when in firstperson, how are you seeing the arm? Talking about the firstperson mod or maybe the paperdoll?

As in I see my shadow on the floor with shaders or when throwing out an item while the inventory is open. Hope that helps.

OH MY GOD....
After nearly an hour I figured out why not having something in your hand while in first-person just breaks the arm smoothing...
The first "player" render call while in that state is the first-person hand, which always gets rendered with pitch 0 roll -0.1 and yaw 0. And since the arm smoothing should only be applied once each frame, it takes only these values(not the correct ones used after that), causing the arms to lock up. While having an item in your hand, the first-person hand is not rendered, bypassing this logic issue.

YOO. I don't know what any of that means but thx for fixing it (: I love this mod so much