Physics constraint with tiny actors

Hi, I’m facing an issue using physics constraint actor in my scene.

I’m trying to create a chain-like succession of meshes linkes with physics constraint actors : a watch at the bottom, a ring at the top.
My meshes are pretty small (less than 1cm), and sometimes the constraints work well, often they don’t.
Collision is disabled in the constraint to ensure this won’t cause issues as I’ve not modelized the collision meshes for now.

When the watch is the start of the chain, it works pretty well - but the watch has to be at the end. However when reverting the order, The constraints only work with 2 objects. When adding a 3rd (and a 2nd constraint actor), nothing moves. Also It looks like I have to space the objects from ca 11cm (measured in ortho view) to make the 2 first meshes react, but the 3rd won’t.

Is there a limitation in the size of the meshes used or something ? Or in the distance between the meshes ?
Using down-scaled cubes works well…
Any idea where my problem could come from ?

Or is there a limit of contraint actor population in scene ?
A previous chain preset that was working before don’t work anymore in the scene now…