UE 5.8.2: Fresh child Blueprint gets Mover overrides and fails to save with "Illegal reference to private object"

General Issues and Bug Reporting (Unreal Engine)
1

Summary

Unreal Engine 5.8.2 (build 56702186, ++UE5+Release-5.8), Windows editor, Mover plugin, existing GASP-based character setup. A newly created child character Blueprint repeatedly fails to save. CharacterMover Movement Modes show overrides even though I have never manually changed them in this fresh child. Resetting these unintended overrides to the inherited defaults allows saving again.

What Type of Bug are you experiencing?

Editor

Steps to Reproduce

Observed workflow in my existing project:

  1. Create a child Blueprint of an existing character Blueprint with a configured CharacterMover component.
  2. Open the child without intentionally editing its Movement Modes.
  3. Observe overridden Movement Modes values and attempt to save.
  4. Saving fails with an illegal reference to a private object in the parent Blueprint.
  5. Reset the unintended Movement Modes overrides to defaults; saving works again.

I have not yet established a minimal clean-project reproduction or isolated the exact operation that introduces the invalid references. The session log shows the initial save after child creation/rename succeeded, followed by repeated save failures after opening the child.

Expected Result

A fresh child should inherit the configured movement modes and transitions and save successfully without requiring manual resets.

Observed Result

The save dialog reports that the child asset failed to save. SavePackage diagnostics identify invalid references from the child’s mode/transition objects to corresponding private objects inside the parent CH_Base_Mover.

Affected objects: BP_MovementMode_Walking_C, BP_MovementMode_Falling_C, FlyingMode (native), BP_MovementMode_Slide_C, BP_MovementMode_Ragdoll_C, BP_MovementTransition_ToSlide_C, BP_MovementTransition_FromSlide_C.

Representative error (package prefixes shortened):
Illegal reference to private object: ‘BP_MovementTransition_FromSlide_C /Game/…/CH_Base_Mover.CH_Base_Mover_C:CharacterMover_GEN_VARIABLE.BP_MovementMode_Slide_C_0.BP_MovementTransition_FromSlide_C_0’ referenced by ‘BP_MovementTransition_FromSlide_C_0’ (at ‘/Game/…/CH_Mover_BattleRoyale.CH_Mover_BattleRoyale_C:CharacterMover_GEN_VARIABLE.BP_MovementMode_Slide_C_0’) in its ‘Unknown property’ property.

Affects Versions

5.8

Platform(s)

Windows

Additional Notes

Workaround: Reset the unintended overrides in the child’s CharacterMover Movement Modes to inherited defaults, then save. This fixes saving in my observed cases, but the issue is recurring.

Investigation: UMoverComponent::MovementModes is an Instanced TMap of UBaseMovementMode objects, and UBaseMovementMode::Transitions is an Instanced array in this engine version. The diagnostics suggest an inherited instanced-subobject/reference serialization issue, but the precise root cause is unconfirmed. It is not yet clear whether this is Mover-specific or a broader Blueprint inheritance issue.

Can Epic investigate why a newly created child can acquire these invalid parent references without intentional movement-mode edits?