I'm no expert but it seems that trail data is slowing down the loading process.
Why do I think it has to do with trail data?
I can only load these maps if have the "Start Paused" button checked.
When the loading starts, the client freezes for about 30 seconds, but then it comes back.
Once it comes back, the game is paused and there are trails everywhere, even though when i made the save I had turned off trails. I turned off trails because the simulation I was running had too many objects.
I think the client is saving ALL of the trail data, then when it loads, it plots all of the trail segments. Even though I saved with trails turned off, when I load, the trails are there and my system is running at < 1 fps. Once I manage to turn off the trails, I had normal fps.
Sorry if this is already a known problem.
EDIT: The simulation I'm running has approx. 250 objects.