Waking both of a constraint's rigidbodies re-enables collisions that were disabled by the physics constraint You can also get this issue to occur by either shooting the two cubes around a bit, or by utilizing the Wake Rigid Body function on the static mesh components for the cubes.

Repro Rate: 4/5

Tested in //UE4/Release-4.27 @ CL#18319896 and the cubes did not collide after being woken, it is a regression.

Steps to Reproduce
  1. Create a new First Person blueprint project.
  2. Place a cube into the scene
  3. Under Physics in the Details Panel, enable Simulate Physics
  4. Create another cube with Simulate Physics enabled and place it over the cube created above
  5. Place a Physics Constraint Actor into the scene
  6. Under Constraint in the Details Panel, set the Constraint Actor 1 to the first cube and Constraint Actor 2 to the second cube
  7. Under Constraint Behavior, enable Disable Collision
  8. Under Linear Limits, set the Z Motion to Free
  9. Under Angular Limits, set all the motions to locked
  10. Place a plane in-between the two cubes and scale it down to 0.5 on all axis.
  11. Rotate the plane by -20 degrees on the Y axis.
  12. Play in Editor and push the cubes off down the slope of the plane.

Results: The two cubes collide with each other even though the Physics Constraint Actor is disabling collision for the constrained actors. (If they fall off and don't collide, move them around a bit to see if they start colliding!)
Expected: The Constrained actors do not collide with each other, following the constraints set by the Physics Constraint Actor they're bound to.

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ComponentUE - Simulation - Physics - Solver
Affects Versions5.05.1
Target Fix5.4
CreatedApr 12, 2022
ResolvedSep 5, 2022
UpdatedJul 29, 2023