landscape loading issues ,,world partition

having issues with landscape loading when using world partition
as per video
it loads fine in the editor and i can navigate all over the world with no loading issues
0 to 1:46 on vid
but when i run the game the landscape is “patchy” with many sections not actualy loading till your over them , and long pauses while its loading
5:mins and on , on the vid

so my first question is , can it be resolved
and 2nd , how ?

i would realy like to use this map as as theres already over 6 months of work put into it ( its manualy lanscaped )

system dell precision 7810 2x e5-2637-v4 3.5gh cpus (8 cores total)
64gb ram 2gb nvme ssd
nvidia rtx 3080 12gb vram