Are you getting stuck at 0% the whole time ?
If so, after the private upload is generated, when it shows you the private version map code, don’t click to continue onto memory calculation yet, the edit/play session will reload, wait till your player is back on the screen, then you can click to continue to the memory calc back in UEFN.
You don’t need to fully switch from UEFN to Creative to see if its reloaded yet, you can hover your mouse over the fortnite icon in the taskbar