The OverlapAll preset changes the CollisionEnabled property to Query only. This means we do not set a simulation flag on the body (for performance). Typically this is what you want because OverlapAll bodies are used for queries not simulation. So what ends up happening is there is no mass calculated by PhysX. To fix this you need to change CollisionEnabled to “Collision Enabled” which will put the body into the simulation. This is indeed confusing and I’ve added warnings to any physics operation (like GetMass or AddForce) when the body is set to QueryOnly.
I haven’t seen this, but it sounds like a bug. Do you mind creating an answerhub post with this?
The welding code is still in early days. This sounds like a bug, but from your description my guess is that you are calling AddForce on an attached object (i.e. the child object). I’m surprised by this behavior though as when calling AddForce on a welded child we actually use the single welded body under the hood. Do you mind making an answerhub post about this too?
Is the child a simulated body? If you try to attach two simulated bodies without welding it will have no effect. The reason is that without welding the attachment says you want to inherit transforms only. However, this is kind of a vague concept when both objects are simulated since the child now has two locaton inputs (PhysX and its parent)