I also thought that it might have been something to do with the geometry. But that didn’t explain why there was no light leak when I navigated the scene in editor, or why camera actors in the level did not show the leak either.
I added the third person game content to the project, just as a sanity check. Used it as the playable character, and there was no light leak:
This confirms your first suspicion that it had something to do with the player character camera. Will troubleshoot settings. and see what I can find.