Alright. So thought I’d come back and let everyone know that I found the problem. It’s a feature, not a bug. For those having this issue:
I finally solved the problem with the disappearing BluePrints: You need to convert the map to World Partition. So first turn it on in your Project Settings, then CONVERT your level (Go to menu TOOLS, then World Partition, Convert Level), once you do that, SAVE, then go to the World Partition Editor, select the whole thing, then click “Load Region from Selection” and NOW it works.