I have the same problem running DX12 on i5-7400 CPU with Geforce RTX4060 8GB VRAM. My map has only a player, a landscape with some buildings from the Pirate pack, Some trees from the Fortnite foliage, and ocaean, a river, a lake and thats it. The game starts and I can run around , but after a while, say 5 Minutes, the game crashes and the white box with the error-message try to allocate more memory, viedo-card a.so. appears. So I think UEFN is not production-ready, so I will switch to UE 5.3 to go on and will forget FN-Dev for a while. Hope Epic will fix the bugs with a stable 1.0 release after beta-phase.