Basically, if the simulation contains particles, it will fail outright and not load (We're working on the fix for that), also we made some changes to how we buffer data with the physics overhauls, and apparently that's caused all bodies to think they are at position 0,0,0 when being saved / loaded.
Saves may be broken for a little while, since we're in the middle of some major overhauls. Hopefully we'll have them back up and running again soon, once things are stabilized a bit more.