frame_id: /systems/isaac-sim-usd-fly-off
The articulation that flew off on spawn
A mobile manipulator was stable in its own Isaac Sim world, but exploded on Play whenever it was spawned as a reference into another world.
Problem
A vacuum-gripper-equipped mobile manipulator behaved correctly in its authoring world, but when spawned as a USD reference into a different simulation world, the entire articulation would launch itself on Play — making it unusable for a spin-up pipeline that spawns assets as references by design.
Investigation
Root-caused via direct OpenUSD Pxr layer inspection. The vacuum gripper's suction-joint attachment was authored with a body0 reference but no body1 — Isaac Sim silently defaults the missing body to the world frame, so the joint's local anchor offset gets baked relative to the robot's authoring-world pose (a ~10 m world-derived value instead of a small tool-local offset). When the asset is referenced into another world at a non-origin pose, the tool frame moves but the joint's world anchor stays fixed; on Play, the stiff drives snap the joint back toward the stale anchor and launch the articulation.
Outcome
Confirmed with NVIDIA as a genuine Isaac Sim 5.1.0 bug, with a fix targeted for the 6.x release. Authored and shipped the interim workaround (deactivating the suction joint) so the spin-up pipeline could keep shipping on the affected version.