Here is attached the test project.
The attachement code is contained in the level blueprint.
All attachements are done during the BeginPlay event.
Then the last one (the blocs on the left is you don’t move the camera) are attached on the first event tick event.
To test and have a reproduction of the behavior, just press simulate.
All the blocs will fall to the ground. Then select the blocs on the second column starting from the left whilst un-possessed and try to rotate them around the Y axis (green one).
You will notice that all the blocs have collisions on the right block.
You will also notice that the two blocs (which are one actor) on the left block have no collision.
Those last 2 are the ones being attached on runtime. And they are the one not having collision.
I deducted that the Weld Simulated bodies worked well in the begin play event or any construction script but would not work at runtime properly, leading to lose of collision on attached components.
I hope that this will help (and if an easy fix exists, please let me now as this would be of utmost importance for our project) and that this is not an intended behavior.
Cheers,
Erio