Hi Gamji,
So I solved it by disabling create compressed cooked packages in the packaging settings which is what “Kleber” (post #11 latest post at time of writing, pretty recently too just a few days ago) said he has done in this forum post: "Ran out of memory allocating x bytes with alignment 0" Error when saving-loading - C++ Programming - Unreal Engine Forums.
I may search why creating compressed cooked packages causes these errors in the stage command, may it have to do what you suggested? Obviously it is desirable to have compressed cooked packages enabled. The packaged project currently stands at 4.35GB which I think is rather large for the kind of game I made. From your points maybe baked light maps might be causing it? I have 2 meshes which I’ve set their lightmap resolution to be 4K cuz they’re massive. But I thought after you bake it it just gets stored in a file and that’s it. Also I used your tip of Size Map and the size of the built data for the level is quite large alongside with blueprints. But I’m not sure that would cause packaging to fail with create compressed packages on.
As for the other points, I’ve removed the majority of unused assets and would like to keep my textures at 4K/2K. I don’t have really high poly 3d assets I don’t think. The textures I use for my meshes are in powers of 2 and I understand they need to be for mipmaps, only the textures which are UI related stuff aren’t, unless these should be too or at least be even numbers to get it to work with compressed cooked packages on?