Simple Join Surfaces not working

I am trying to build a basic box model made up of parts using Join Surfaces.
In the build picture the right hand box has some parts moved out to show the skeleton structure.
When I run the boxes collapse.
I have tried using Weld Constraints instead of Join Surfaces but get the same collapsed boxes.
Is this ‘feature’ of Join Surface a bug?
Pics
Build

Run

1 Like

Have you tried anchoring your build?

I’m pretty sure join surfaces automatically makes welds in the parts, but it appears your objects have none. I feel like it was you doing something wrong. What did you do to use it? I’m pretty sure you use it in the creation and it will autoweld the parts you’re adding together.

Woops.
Anchored all parts and the box’s stay built.
So maybe jojn surfaces is working.
Is there any way I can check?
For example could I search for the welds in the model?