I do not know what may be your issue but it could be that the cells were unloaded. So in the partition window select the cells and right click to load cells.
I recently made a video going through a lot of these steps, maybe it will help you.
yes the cells get unloaded automatically when reopening… this is intended,… the purpose is that you don’t want everything loaded at once when opening the map, especially when your world is full with stuff and super heavy…
so just go to your “world Partition” window… select the cells,… right click and load… there you can also choose to load all and so on