Wish that were true.
Working in 5.4, I created a level with 2 of 16 regions loaded, I placed objects above and below landscape (cave), saved all and exited. The next time I open this level, not all objects are loaded; some are others are not. I found one possible reason: Objects that are occluded by others (so actually invisible) I can understand and can be deleted from the scene, but others are clearly visible but are also unloaded, where other, adjacent objects are loaded. It always are the same ones, every time I open the level, randomly located in the outliner. Switching to another level and reopening the one I’m working in renders them again ‘unloaded’, even if I pinned them.