It does happen with other limbs. There is what happens if I attach the other limbs, in the file I haven't attached all arm and leg, parts all the way through. But I think you can see what happens. It seems to happen randomly.
Error Log from this:
Godot Engine v3.4.beta.custom_build.c09dc540f - https://godotengine.org Godot Engine v3.4.beta.custom_build.c09dc540f - https://godotengine.org Godot Engine v3.4.beta.custom_build.c09dc540f - https://godotengine.org OpenGL ES 3.0 Renderer: NVIDIA GeForce GTX 1060 3GB/PCIe/SSE2 OpenGL ES Batching: ON ERROR: Index p_column = 1 is out of bounds (cells.size() = 1). at: is_selectable (scene/gui/tree.cpp:452) - Index p_column = 1 is out of bounds (cells.size() = 1). ERROR: Index p_column = 1 is out of bounds (cells.size() = 1). at: set_icon_modulate (scene/gui/tree.cpp:212) - Index p_column = 1 is out of bounds (cells.size() = 1). ERROR: Index p_column = 1 is out of bounds (cells.size() = 1). at: is_selectable (scene/gui/tree.cpp:452) - Index p_column = 1 is out of bounds (cells.size() = 1). ERROR: Index p_column = 1 is out of bounds (cells.size() = 1). at: set_icon_modulate (scene/gui/tree.cpp:212) - Index p_column = 1 is out of bounds (cells.size() = 1). ERROR: Index p_column = 1 is out of bounds (cells.size() = 1). at: is_selectable (scene/gui/tree.cpp:452) - Index p_column = 1 is out of bounds (cells.size() = 1). ERROR: Index p_column = 1 is out of bounds (cells.size() = 1). at: set_icon_modulate (scene/gui/tree.cpp:212) - Index p_column = 1 is out of bounds (cells.size() = 1). ERROR: Index p_column = 1 is out of bounds (cells.size() = 1). at: is_selectable (scene/gui/tree.cpp:452) - Index p_column = 1 is out of bounds (cells.size() = 1). ERROR: Index p_column = 1 is out of bounds (cells.size() = 1). at: set_icon_modulate (scene/gui/tree.cpp:212) - Index p_column = 1 is out of bounds (cells.size() = 1). ERROR: Index p_column = 1 is out of bounds (cells.size() = 1). at: is_selectable (scene/gui/tree.cpp:452) - Index p_column = 1 is out of bounds (cells.size() = 1). ERROR: Index p_column = 1 is out of bounds (cells.size() = 1). at: set_icon_modulate (scene/gui/tree.cpp:212) - Index p_column = 1 is out of bounds (cells.size() = 1). ERROR: Index p_column = 1 is out of bounds (cells.size() = 1). at: is_selectable (scene/gui/tree.cpp:452) - Index p_column = 1 is out of bounds (cells.size() = 1). ERROR: Index p_column = 1 is out of bounds (cells.size() = 1). at: set_icon_modulate (scene/gui/tree.cpp:212) - Index p_column = 1 is out of bounds (cells.size() = 1). WARNING: BaseButton's Enabled Focus Mode property has been deprecated due to redundancy and will be removed in Godot 4.0. Please use Control.set_focus_mode instead. at: set_enabled_focus_mode (scene/gui/base_button.cpp:329) - This method has been deprecated and will be removed in the future. undo undo ERROR: Condition "_first != nullptr" is true. at: ~List (./core/self_list.h:108) - Condition "_first != nullptr" is true. WARNING: ObjectDB instances leaked at exit (run with --verbose for details). at: cleanup (core/object.cpp:2069) - ObjectDB instances leaked at exit (run with --verbose for details). ERROR: Resources still in use at exit (run with --verbose for details). at: clear (core/resource.cpp:417) - Resources still in use at exit (run with --verbose for details). ERROR: Condition "allocs_used > 0" is true. at: cleanup (core/pool_vector.cpp:63) - Condition "allocs_used > 0" is true.