If you use any _create function except ent_create (so if you create panels at runtime or something like that) you sadly cannot use game_save.
All what I use is "ent_create" and "ent_createlayer". But, I'm sure they're not the problem
What kind of game are you working on, what type of levels do you have?
I am working on a normal 3rd person shooter game. Concerning the levels ,I don't know what you mean
Oftentimes it's just better to write your own save and load system.
I think that will be a little bit difficult but how to do it?