Editor freezes when editing sub-level referenced by more than one level

This bug occurs when more than one level references the sublevel.

Occurs in 4.18P4 CL 3676890
Unable to reproduce in 4.17.
This is a regression.

1. Create new Blank Project, no starter content
2. Create 3 levels named A,B,and C
3. Save All
4. Open Level B, make Level A a sublevel of Level B in Levels Panel
5. Open Level C, make Level A a sublevel of Level C in Levels Panel
6. Open Level A and place a few Actors within it
7. Save All
8. Open Level B or C, then return to Level A
9. Delete, Cut or Rename any actor within the level

Result: Editor will "freeze" in Updating Asset References
Editor is unable to be closed normally, but does not appear as "Not Responding" in Task Manager

Expected: Selected actor will be deleted or renamed