Not sure what happened in UE 5.1 update but, now we need explicitly package maps. Go to Edit/Project settings Project/Packaging add maps to the field List of maps to include to packaged build. https://forums.unrealengine.com/t/5-1-open-level-by-name-node-does-not-work-in-a-packaged-game-it-brings-back-to-the-same-level/694199